1974 Duster 340 Engine and 727 Transmission Questions!!!

727 is a better transmission but for the 340 the 904 will handle almost anything if built or rebuilt with the 340 in mind.

also the 904 will give you more clearance and same drive shaft. If you go that route. The 727 if built well is a fantastic transmission but heavier, physically larger and in an later a-body like a 67-76 makes exhaust fit ment a tad tougher.
IMHO.