The 7.5" stock rear will also be a time bomb. Exploding spider gears first followed by everything else, depending on the power level. I broke a Power Trax No Slip and then the stock spider gears behind a mild Olds 403. The TKX is great trans but big dollars. I just picked up a used 4L80E, also not cheap these days. As said for the TH400, a slightly shorter driveshaft, possible frame extensions, depending on the year and an electric kick down switch. You also probably don't want the stock converter, even with a mid 70's smog 455. You will need a drop base air cleaner and short filter due to the taller deck height. Good luck.
