Motor Match up
The 21 and 22 series machines use the same exact motors and pump parts. They only work in those models The 23 was the first of the whirlpool Powermodule style pumps and as has been mentioned many times on this forum, WP made the opening in the tub smaller to accommodate the Powermodule.So they are not backwards compatible.
Here is the part number you need to look for: 4163523 which covers both series. It is also the part number for the pump motr, seal and start relay.
If you are in need of a motor, I have a couple of used ones that I am willing to part with. Sorry, but the complete one NIB stays with me. At least for the time being.