looks like a 21
to me. i don't have a 21 superba but i have a 21 and that top panel looks awfully similiar. if it's a 21 it was made from 84-89 according to my production chart.
as steve said parts are around, just have to hunt a bit and put the word out. it prob will run fine, i have only had to replace one seal out of all my kitchenaids, including some from the 50's. and those motors are built to last!