Hi guys I have done a lot of looking at early CJ's that have done this conversion that started out with the same Ross box and switched to the later saginaw units both power and manual. There are many more power conversions than manual. There is really no clean way of swaping out the Ross for the Saginaw without causing some damage to the frame and or tub.
I have seen the Advance Adapters kit and several other companies kits. Most are designed for power steering which requires some pulley changes and brackets added to the motor.
Many I have seen are in early Jeeps with iron duke V6 conversions and use GM parts.
I have yet to come across a kit for the manual box for an M38A1.
I have seen several M38A1's with both power and manual Saginaw boxes but they were home grown conversions and were not done with alot of care to going back to stock and they utilized faricated front bumpers and frame mounts and some altered front spring shackles that almost always needed some cutting and boxing of the frame.
I picked up a NOS manual saginaw box and the Advance adapter kit at a swapmeet. The adapter is for the power steering swap which I do not think will work easily with my plan in not doing unrepairable damage to my frame and or altering my engine compartment from the military parts.
One of the painful things that you need to do is cut the steering column and add a joint so that you can change angle of the shaft since moving the box out in front of the radiator makes for a geometry change in the shaft angle and length.
Borgeson seems to be what eveyone uses although I did see a couple of GM rag joints.
Because my M170 is a late model USMC and rust free and all original I have come full circle back to buying a government rebuilt Ross box and just living with the sloppy steering. I will replace all the rest of the steering componets with the best NOS GI parts I can find and hopfully it will be a little better out on the six lane interstate.
When I am off road I hardly notice the slop because of the slow speeds and the terrain.
One of the things about the Ross boxes everyone has for sale is that you need to give them a core for the price you see advertised.
I would like to keep my original box so I will start looking for a detached Ross box to use as a core.