Not familiar with the SM420, but I know it is not the easiest thing to adapt to the D18 and v6. Easiest way to do this is a T18 with a ford input shaft and a large hole D18. The stock 225 v6 bell can be drilled and tapped for the T18 mounting holes. You would need a T18 with a "texas" pattern on the back side. This is what I did for my jeep.

I would likely use the SM465 because it is the shorter package and gives you a longer rear driveshaft.  You would have to get the index machined on the BOP bell.  Downside is that it is 40 to 50 lbs more than the SM420.

Also, don't waste your time with the D27.  I've had more problems with those than the D25's.  May as well just go for a D30 that is definately an upgrade.  I believe 76-86 have discs.  The rear D44 should at a minimum be the 19 spline version.  Better would be Herm's 30 spline full floater or the rare as hell 70 1/2 - 71 30 spline flanged axle.

I would also be boxing the frame but that would depend on the anticipated use.

PROGRESS...

I bought a newly built 225 V6 (Offy DP intake, Sanderson headers, Comp Cams RV grind, new lifters, pistons, etc.) from a member on the earlyCJ5 BBS. Now planning on a Ford T18 with advanced adaptors short bell housing. I will need to sort out frame mounts for the motor and trans, etc.

Here's the engine:

Bill04SD wrote on 06/21/14 at 23:28:34:


That's a good idea... any idea how much trouble it is to fit a 2A tubs to the CJ5 chassis?

The frame from an early CJ5 will easily work under a flatty body. The frame rails themselves are identical with the exception of an extra 2-1/2" of length on the front horns, and 3" extra on rear. Crossmembers, spring hangers,  and shock mounts are located a little differently, and the front crossmember is rectangular instead of round. Body mount brackets (those that weren't omitted at the factory) are in the same place.
The only downside I see to using a 5's frame under a flatty is the extra length. It may not be obvious in the front, but having the rear crossmember sticking out 3" just isn't right. and you'd lose the rear body mount locations.
I started to modify a V6 CJ5 frame to a 3's dimensions when I found bigger issues with 5 (paper thin in spots). Have since repaired the 3A frame and have it at the sandblaster now.

As far as I know, 3A and 3B frames are interchangeable.  Modifying a 5 frame is not that hard if you end up having to go that route...contact me if you do, and I can provide some details.

It's not to hard to modify the 5 frame to get the crossmember back under the body.  As stated above you really don't notice the extra length up front.  I've done two flatfenders now with CJ5 chassis.  Both of the ones I did used 1970 CJ5 chassis so I also picked up the dual circuit master cylinder as a bonus.