Buffalo Enterpises makes an adapter palte to bolt a leter automatic to the 235. While the TH350 will work fine, you might consider the TH700R4, which has a better first gear ratio as well as an overdrive gear. You will need to go to an open driveshaft, the easy way would be to swap the 3rd member/torque tube of your existing rearend out for a 3rd memebr from a '55-'62 1/2 ton truck and weld up the pivots. That will allow you to keep the proper width rear and yur 6 lug wheels.

Bill Burmeister