You need to be aware there are some rough spots inside the TH400 case casting that probably won't meet your quality control standards. They don't affect operation, however.
It's an extremely strong transmission, but it absorbs a lot of power internally. The power loss when adapted to a 235 would be considerable, resulting in poor performance and marginal gas mileage. I think the major difference in the transmissions used behind the diesel engines was a torque converter with a different stall speed, and possibly clutch drums that would accomodate one more steel and fiber disc for better torque capacity. The 4L80 transmission is basically a TH400 with an overdrive added, plus a lockup converter. The TH400 is good for heavy loads and towing, not so great for use with low-torque engines and/or fuel economy.
Jerry
