i just took out a 518a OUT OF a 1948 dodge street rod we are working on,,other then the over drive unit,, it didnt appear to be as big as a normal 727 body,,
If it was a 518 it is as big as a 727 because the main case is based on the 727 case. The A500 is based on the 904 case so it's smaller. I've seen them side by side and each main case is nearly identical as the corresponding non od unit. The O.D. unit is alot bigger than the original tailshaft extension. That's where the problem with fitment comes in.