Gears for a 1972 Chevrolet Chevelle?

I need new gears for my 1972 chevelle. I'm cruising down the highway at 65 mph and my engine is revving at about 3000 rpms. What gears do I need (3.08, 3.55) in order to cruise at 70 mph at about 2000 rpms? I don't know the current gears (just got the car last week). If I get the correct gears, will I be able to cruise at 70 mph at about 2 grand AND still have enough power to smash down on the gas and go as fast as I want? its got a 383 stroker in it. Thanks!