OD trans behind a 273

Another factor to keep in mind is that you might need to have a custom torque converter made. From my reading here it is my understanding that the register in the crankshaft changed the same year the number of input splines changed on the automatic transmissions. When putting a late engine in front of an earlier transmission there is a spacer that you can purchase to fill the gap but options for a late transmission with an early engine are limited.