There are 2 different automatic transmissions for the /6, depending on the chassis. Compacts get the small 904, full-size cars and trucks get the stronger 727. Both can be upgraded for reasonable power levels but the 727 (longer, heavier) won't need anything but a shift kit (I use TransGo) and a converter, the 904 uses less power but gets expensive very quickly.
What I'd be looking for: a wrecked Dart Lite or Feather Duster, which have 225 engines with aluminum intakes, and 3 speed + overdrive manual transmissions (based on the very strong A833 used in the 440 etc.).
Ratios:
1st 3.09:1
2nd 1.67:1
3rd 1.00:1
O/D .73:1
