My 78 has the 3.54 and I have a really nice NA five speed thats pretty much ready to go.
As mentioned I bet its really nice with a turbo motor to have really long gears, Itll also keep RPMs down on the highway.
My question is how much of a change in the rear end will be beneficial, at some point if you go to to high of a gear youll loose most of your ability acceleration. It would be nice to know where that point is...