IMO the M20 has the best ratio for 1/4 mi runs. You could buy the M22W gears but I found out that the whine isn’t as loud as the GM Masario gears bc the gears are cut on computer operated machines.
Did the seller have the protecto plate to go with the car? One of the few original items I have with my 71 Camaro (350 L65, 4 speed, F41 package) is the protector plate. That has all the major options on it. My Camaro came with the M20 Saginaw. After upgrading the clutch to an 11 inch plus headers, Torker intake and Holly 700DP that transmission was toast. Replaced it with a Muncie M20 and Hurst Super Shifter. The M20 first gear was a better choice for the 3.08 gears in my rear end.
But my 71 Big Block Chevelle came with the M22. Loved that trans!