904 or Powerglide???

If you can swing it I'd go with the 'glide. Converter selection is critical. That gear may be OK depending on the trap speed. With that small of a tire and that light of a car the 'glide will be a better choice. It will launch and hook much more consistently. The 3 speed (904 only, forget the 727 altogether as it's too big and too heavy) would be a better choice for a car weighing over about 3000 pounds.

The best way to accomplish the swap is with a LA small block to PG Ultrabell from JW transmissions in Cocoa Florida.