I cleaned it and opened the side cover; it is apparently an M20 (from the 2 grooves) although I didn't spin it and count turns. It is NOT an M22.
I've never ran the transmission, although I've had it since 1971; installed it briefly in a Henry J, but it was only ran once around a short block. I let a friend use it for a few months back in the late '70's in his 55 Chevy. All the numbers from the parts seem consistent with '68-'69 Muncie production, although I know I did swap the front case after I purchased it... so we know the front case came from a April or May '68 Chevelle (Kansas City plant). All visible characteristics of the trans are consistent with '68-69 Muncie M20/M21.
The ears and gears look good, and there is no damage, existing or repaired, to the transmission cases. The Chevelle VIN is stamped on the top of the transmission. I need Camaro $$ more than I need this trans. Do you have any idea what it's value would be?