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Chad, which rear gears are you running? For street use, the Muncie M20 wide ratios are much better than the M21/M22 close ratios. I currently have the M21 with 3:55 gears and hate it. First gear is too high for fast acceleration, and fourth revs to 3000 at 70 mph (which is borderline high.) The rock crusher is the M22, but be aware that it's very noisy and very expensive. For close to the same money, you could get a Tremec or Richmond 5-speed. The Richmond 6-speed is also nice, but it's more expensive than the others.
Unless you want to finish the return of your car to it's original state. In that case, see if you can find out which transmission originally came with the car. Suppose only way is to check the tank sticker. My guess is the wide ratio M20 was probably more popular with the big block and the close ratio M21 more popular with the higher revving, lower torque small blocks. Get the Hurst shifter though...much better than the stock one!