I also know a good bit about mopar, but I doubt that you will be able to adapt a 70 318 to a 50s tranny. The bell housing is on the tranny is MOST LIKELY different then the bell housing that the 70 318 would mount up to. If so, then the starter wont be able to match up correctly. Why dont you just find a 50s dodge with a 318 and 3 spd tranny to transplant into your 24 roadster? Lemme know how it works out for ya.
Drew