Len,
As you know, the M22 (and the M21) have 2.20:1 first gears. Your old M20 had a 2.52:1 first.
I imagine your theory was that the torque of the 454 would easily overcome the difference. Now you're not so sure.....is that correct? Is it sluggish out of the hole?
The M21 / M22 gears were best suited to hi-reving Special Hi-Performance and Heavy Duty engines. Is your 454 one of these?
Have a look at this comparison sheet I made up when I was deciding which rear gears to use with my Richmond 5-speed (3.28:1 first). Maybe it will help you make a decision about which transmission.