724jacks

I drove my 71 chevelle with 3.31s and an m20 for a while, and it was OK. I won't go any numerically lower than 3.23. Another option if you want a 4 speed would be a 2.88 1st gear ratio super t10. You could run a 3.08 in the rear and first would be similar to the m20 and a 3.42 rear.

Just my .02

Good luck

Here is a link with t10 ratios
https://www.chevelles.com/threads/su...-ratios.23335/