Different Gear?

My 74 Duster has freshened 74 cast date stock bore 318. I bought the engine carb to pan after it was boiled and built by a third party I can not locate.
Here is what I know about the motor. The bottom is stock. The cam is a Mopar performance piece that produces .480 lift. The heads are 1974 cast date 318 heads with a fresh 3 angle 1.88/1.60 valve job with nice porting and blending work. Intake is Edelbrock Performer gasket matched ported to heads. Exhaust manifolds are 1970 340 high performance pieces also gasket port matched. Carb is Edelbrock 1406. Ignition is recurved stock electronic ignition distributor with Petronix Flamethrower HEI. Exhaust is 2.5" straight old school dual with Thrush welded mufflers. Torque converter is the stock "high stall" unit used in the 1970 Duster. A true budget set up, but I gotta say the car goes like hell!
The rear is an open diff 8.25. I want to get a suregrip unit and some gears that will perform better than the highway gears I have now, although I like how the car drives on the highway!
What would you do?
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