76 F250 Highboy swap to 351M

[xaos1964]

Long story. Restoring my late fathers 1976 f250 4x4 highboy. Years ago he replaced the OEM 360 with another. Kept original trans but with a married transfer case. Eventually parked the truck in the field where it sat for 20+ years. Two years ago I pulled it out of the mud, stripped the mechanical and electrical, & sent the body to the shop for restore. Had a 351/400 M rebuilt with another C6 trans. Installing the original divorced NP203 chain transfer case. Rebuilt.
I get the truck back, bolt the transmission to the engine, slide both into place and wtf?? rear transmission mount is 3 inches forward of the crossmember. I swap the motor mounts side to side, which brings the engine back, but it's still almost 2 inches forward of the crossmember.
Any idea of what's going on with this? Engine is an engine and there shouldn't be an issue with the motor mounts. Are the towers different for a 351M? Or is it possible there's a longer trans tail assembly that should be installed?
Any ideas would be appreciated and Happy New Year

[two-bit]

Yes, there are different perches, and different locations for those perches.
I do know that the FE block and I-6 block used the same perch in the same location.
Small block engines use there own perch in a different location than the FE/I-6 location.
351M/400 engines i am not sure about. I know they use a different location than FE/I-6. It maybe the same perch, just bolted in further back, i am not sure. Don't know much about the in's and out's of those engines.
On a brighter note, those engines were used in the highboy chassis. So there should be info out there as to which one you need and its proper location.
Two-bit

[basketcase0302]

"xaos1964"Long story. Restoring my late fathers 1976 f250 4x4 highboy. Years ago he replaced the OEM 360 with another. Kept original trans but with a married transfer case. Eventually parked the truck in the field where it sat for 20+ years. Two years ago I pulled it out of the mud, stripped the mechanical and electrical, & sent the body to the shop for restore. Had a 351/400 M rebuilt with another C6 trans. Installing the original divorced NP203 chain transfer case. Rebuilt.
I get the truck back, bolt the transmission to the engine, slide both into place and wtf?? rear transmission mount is 3 inches forward of the crossmember. I swap the motor mounts side to side, which brings the engine back, but it's still almost 2 inches forward of the crossmember.
Any idea of what's going on with this? Engine is an engine and there shouldn't be an issue with the motor mounts. Are the towers different for a 351M? Or is it possible there's a longer trans tail assembly that should be installed?
Any ideas would be appreciated and Happy New Year

Sounds like a really nice build! And to keep the truck in the family kudos to you!
To start with if he never changes the engine "towers" (frame mounts) it might be part of your problem as they are different from the 360 to the 351M shown here:
http://www.fordification.com/tech/engine-perches.htm

And I can also confirm there are multiple tailshafts for the C-6 tranny but don't believe there are different version in the married version, (believe you said it is married to the NP-203 right)?

But not a disaster even if you have to move the crossmember as i did it to accomadate the 302/C-6 combo into my 71'DRW flat bed from, A 360/NP 4 spd.
I believe there are 8 steel rivets if memory serves me right, (holding the right angle braces part number 5098 riveted to the frame rails-that the cross member rest on/bolts to) and then it should easily slide foward to where you need it, (part number 5028 in this image).
I'm not 100% sure if your F-250 4 X 4 will be the same as the 2WD but worth looking at.

[cep62]

there are multiple tailshafts for the C-6 tranny but don't believe there are different version in the married version,

Not related to thee O P 's question but there are two different length output shafts for married T cases.
78, 79 Broncos used a longer tailshaft. I'm not sure why , maybe weight distribution with a short wheelbase. ?
And I had a 78 F250 with the long shaft but I don't know if it was stock.

[two-bit]

I just looked at that link.
I have a set of engine perches that came out of a '78 F-150 4wd 351M engine.
Not sure if they will work in your highboy frame.
I can look for them later this week and see if they have any part numbers on them.
Couldn't tell you the build number on that truck, it got parted out a few years ago.
Two-bit

[two-bit]

there are multiple tailshafts for the C-6 tranny but don't believe there are different version in the married version,

Not related to thee O P 's question but there are two different length output shafts for married T cases.
78, 79 Broncos used a longer tailshaft. I'm not sure why , maybe weight distribution with a short wheelbase. ?
And I had a 78 F250 with the long shaft but I don't know if it was stock.

I know they did that with the NP435 4spd. Truck vs Bronco was different length. Not by much, but still different.
Back to O.P., he stated he was running a divorced 203. So pretty sure this is a mute point, except for sharing info.
Two-bit

[xaos1964]

Thank you all for your responses. Much appreciated. Will try to address everyone here.
First, The build I'm doing is with the original Divorced Transfer case. I'm not sure if there's different lengths for the C6 tail shaft. I do know there's three different versions of the C6 used though depending on the engine you're using.

Two-Bit; thank you. I wasn't aware that the 351/400M was used in the highboy. I'm guessing in earlier years. Any idea where I might find the information? I know Green sales might be one. I really don't want to go hacking this in as I'd like the unit to stay as original looking as I can.
I'm pretty sure though that the towers from a 78 wouldn't work. The 76 highboy had a more narrow frame set up than the later 77's through to 79. I found a guy on e-bay that has a set from a bronco/F150-F350. They look like they might fit but want to look into it a bit more before purchasing as they're 400 USD, ceramic coated and ready to install. Will recheck the frame to see if the existing perches can be moved back.

Basketcase302. Thank you very much. It's coming along very nicely. Will post photos if I can. Was actually first truck I was driving on the farm, then my brother and sisters. so kinda hard to see it go to waste.
Towers were never changed, so assuming that's the problem. I'm not sure about the tail shafts for the transmission. Guy that redid this trans says there's not another option for the unit. But will look into that as well again.
2WD is different from 4wd mounts. On the 4wd highboy, the towers are mounted to the frame only. Not the frame and crossmember. The link you sent didn't show the 4wd in the 76 highboy that I can see. Part numbers I was given are as follows. **D7TZ-6028-A for right side and D7TZ-6029-A for left. The later 77's and 78's used a different number yet, but it looks like just a revision change so they may work too- D7TZ-6028-D (right) and D7TZ-6029-D (left).**

Again, thank you all and Happy 2021.

[xaos1964]

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[xaos1964]

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Photos of the unit so far.
Upgrade to the electrical in process. Will replace front to back with modern electrical system. Includes all switches. Will also install modern instrument cluster. Finally, fuel injection conversion kit.

[bellamor]

I am seeing the progress with this build. I am honestly excited to see how it will turn out.

[xaos1964]

Thank you. I'm anxious to get it done. But that's gonna be a bit. Covid had me out of work so time was being spent mostly looking for work. I'm guessing late summer before it's finished, but will post pics as I get bits done.