Got started on the project this week. Pulled the slant6 and trans out.
Going with a Cummins 4cyl turbodiesel, and TH400 trans.
Trial fit of the Cummins shows it almost sitting right on the /6 motor mounts. The bolts line up and start in the holes, but the pan hits the crossmember and steering draglink. It looks like the mounts can be moved back a couple inches, I'll try that and see what happens. I may need to raise the mounts up a couple inches. The other option is getting the proper mounts from Dodge, but what fun is that?
Amazingly the rubber motor mounts appear to be the same on both motors.
I'll get a couple pics when I test fit the motor again.

 

does the th400 tranny bolt right up to the cummins? and is yours just going to be 2wd?

 

I got mine with the TH400. There are flywheel housing adapters to allow the Cummins to bolt to almost anything. What are you looking for? Yeah, mines 2wd.

Heres some pics:

 

some day I would really like to convert my 76 power wagon to a cummins but I really want the 6 cylinder for better pulling, Im probably just going to buy a 1st gen doner truck that has a bad frame or something like that. I really like your project tho keep us posted as you go.

 

Nice man! Good luck with her, should be interesting to see the final result.

 

What are you planning to pull? These 4cyls are in a lot of 1 ton step vans, where mine came from. Either one is a great motor. The 4 will get better mpg's.

So, after another test fit, I need to modify the motor mounts and crossmember a bit. In some step vans the motor is slanted a little to allow clearance for the drivers compartment. I have one of those. I need to raise the right side of the motor about an inch, and the left side about 2", to level the trans. I want to use the rubber motor mounts, so I'm using 2 1/2" plates sandwiched around the right mount to lift that side an inch, and using a section of 2"x2" box tubing to raise the left side. The crossmember will be slit lengthwise on each side, and an inch or so cut from the back side, then drawn down, welded back together, and some filler panels added. This is due to needing a little more clearance for the oil pan, and to allow easier install of the motor.

 

Time sure has flown. I didn't realize that I hadn't updated my project, so here it is.
I ended up rebuilding the motor mounts, moving them further back to better support the weight of the Cummins.
The motor had a 8* tilt in the step van, it is now 4*, split between the motor and trans. I had to get a 6bta exhaust manifold, cut 1 cylinder off each end, and cap it, to get the turbo into a place where it would work.
I had to build a crossmember for the trans.
I eliminated the brake booster, because I had no vacuum source, but that resulted in a hard brake pedal with little stopping power. I went to a smaller bore master cylinder and as soon as I can get a little help to bleed the brakes I'll know if that worked.
Hopefully it will and it will get inspected and driven daily.
It is now moving under it's own power.
Here's the build pics, start to now.
http://i114.photobucket.com/albums/n...s/P1020519.jpg
http://i114.photobucket.com/albums/n...s/P1020520.jpg
http://i114.photobucket.com/albums/n...s/P1020521.jpg
http://i114.photobucket.com/albums/n...s/P1020654.jpg
http://i114.photobucket.com/albums/n...mins/001-2.jpg
http://i114.photobucket.com/albums/n...mins/003-2.jpg
http://i114.photobucket.com/albums/n...mins/004-2.jpg
http://i114.photobucket.com/albums/n...mins/005-1.jpg
http://i114.photobucket.com/albums/n...mins/001-3.jpg
http://i114.photobucket.com/albums/n...mins/002-3.jpg
http://i114.photobucket.com/albums/n...s/P1020763.jpg
http://i114.photobucket.com/albums/n...s/P1020759.jpg
http://i114.photobucket.com/albums/n...ps546bb4c6.jpg
http://i114.photobucket.com/albums/n...pse08f1550.jpg
http://i114.photobucket.com/albums/n...ps5a21d608.jpg

 

Nice. Looks like a clean conversion. Is the truck staying orange, or going plum crazy?

By the way, what gear ratio is in the truck that you decided to keep the 3-speed auto?

 

It will get painted "Plum crazy" later, right now I just want to drive it!
Went with a 2:55 rear ratio. That should put me around 1700 at 60mph, right in the Cummins power band.

 

2.55 or 3.55? I've never heard of a 2.55 for the 9.25 rear end...

Looks side either way.