Rear ends - explaination

You have to get one from the type of car you have. ie: a-body OR you can get one from a b,c,e body and have it narrowed to fit your a-body Duster. If you get one get the brakes (all of the brakes) with it as it will save some hassels later.
As far as a street/strip car and gear selection, a set of 3:91's would work good with 4:10's being the very biggest gears if you plan to take it on the highway much. Even then the 4:10's are a little much.

Jack