"... How about to 3.55? is the change drastic or minimal?..."
I'd call a change from 3.08 to 3.55 drastic. But, 3.55's work good with a 4-speed. The 3.73's will give you more acceleration, but will increase your freeway cruising RPM up to well passed 3000 rpm.
A 3.23 would probably be about the best compromise, if you do a lot of 70mph cruising. I suppose. The late 2nd gens used the 3.23's and 3.42's, with the 4-speed.
Oldskool He has a m21 he is wanting to use. It has a 2.20 first gear unlike the m20 2.56. Pulling out with 3.23 will be a dog. GM would not use gearing higher then 3.70 with a close ratio Muncie. Must options were only allow 3.73 through 4.11
I would not recommend anything anything higher the 3.73 .
