The M22 Munci has a fine spline input shaft and the output shaft is the same size as the T400. The M21 have the coarse spline and the output shaft is the same a T350/powerglide. The double rings on the input shaft usually indicated a close ratio. I had a single ring which had the lower 1st gear ratio which made it nice for the heavier car.
Most of the M22's have the straight cut gears and would be a little noisy for the street, but I do know that in 1973 the Corvette had a fine spline input and T400 output with the heli-cut gears. I purchased it from the owner of the Vette when he went to a Doug Nash 5-speed. That was the best Muncie that I ever owned and when I purchased it, it was in pieces and several buckets.
Stay far away from the Saginaw, because they are super weak. The T-10's are good and I think that there was 1 version that even came in an aluminum case.
I would recommend a steel flywheel and a shatterproof, if you can. I had a flywheel explode on me once and luckily I didn't get hurt, but it is like a grenade going off.
Good luck,
Bill M