As a owner, builder and racer of many different Mopars, 318, 340, 360, 383, 426M.W.,426 Street Hemis, 440 and so on the most fun street car, and fastest was a 400 block pump gas stroker motor, 512 C.I. and then 518 C.I. in a 1971 Duster With your goals I would put a 512 stroker, 400 block with a 4.250 stroke crank with after market forged steel H beam 6.700 BB Chevy type rods Put a 3.54 gear in the Dana and go have some fun with good mileage, if you can control the right foot to get good mileage My 512 pump gas stroker, which became a 518 C.I. later with a crank swap to increase the stroke to 4.300 to get some more compression after changing the iron 906 heads for a set of Eddy RPM heads was a blast to drive and way faster and more powerful than I had hope for With the Eddy RPM heads and a low deck sixpack intake and carbs. with 10.29 to 1 compression ratio with the 4.300 stroke that motor made over 700 HP at 5600 RPM and similar ft. lbs of torque at 4500 RPM on Oregon pump gas With the big C.I. stroker mtors you can run the RPM a lot lower and still have way to much torque and HP for most street tires