The T56 doesn't fit easily into an older Mopar. Besides, with a 512 stroker you don't really need a 6 speed transmission. You'll have enough torque to work with a 5 speed. Best bet is probably the Passon 5 speed. Everything else is a bit of a compromise. If I was doing it all over again I'd either go with the Passon 5 speed or take a serious look at the 6 speed auto.