Cruise friendly low 12's with a 340 Dart

Just to toss out another angle, run 4.10 gears with your 727 and put a gearvenders OD unit on it. That will drop it to a 3.20 for the highway. Not terribly low buck, but meets all the other criteria.

This thread has me all inspired, as my set up will be quite similair( I took the OD unit off my F250) and I was wondering how it would run. Keep us posted on how it works with the combo you choose please!