A518 46RH rebuild

The main problem I think you'll have trying to run the old style 727 mount and crossmember is that I "think" the whole setup will raise the rear of the transmission too high, throwing off driveline angles. You may end up needing to cut the center out and fabricate a new flatter center like one of the two I have shown. I suspect the large diameter of the overdrive unit required the shape change in the crossmember to get the angles correct.