727 without a doubt. Even built up 904s break too easily. If you go for the OD auto, make sure to get the 727 version, and install a big trans cooler.

A 4 speed or 5 speed OD would work too, but they are more work to get right in most rods.

The chopped top just doesn't work for me, I think it makes the car look out of porportation. Most 40s & 50s already look too long to me, the chopped top makes them look even longer. Gene