The M21 in my 69Z is going to need a major rebuild in tne near future. I was looking at a website www.5speed.com that sells new and improved M22's for First Gen Camaros.
I know M22's gear wind-up sounds awesome but are they really better then the M21's

You should go with a 5 speed like a Tremec TKO.

You should go with a 5 speed like a Tremec TKO.

Yes, there are many options out there for a replacement transmission. There are 5 and 6 speed kits to chose from. But, to answer your question, an M22 is stronger than the M21 due to the different helix angle gearset in the M22.

And those brand new M22's have stronger main cases thru better and thicker castings, iron mid plates instead of the weak aluminum ones, and a stronger cast tail shaft housing.This new trans will take alot of abuse. I run mine hard launching at 5000rpm's and havent broke it yet.The manufacturer is a company called Autogear.You may want to check their website and see if you can buy cheaper directly thru them.