TH-425
3 speed auto, came in Oldsmobile Tornados and FWD GMC motorhomes.
Most of the mods you can do to a TH-400 will work on a 425.
They would suvive with a big block in a motor home, so they should handle 300+ easily.
Lincoln Lock FTW.
On my POS I have BFG AT/KOs and they did very well in the snow last year. Very tolerable road noise. Just throw some weight in the back and you should be golden.