Hi Gary
This damage is as you probably guessed caused by the universal joint bolts getting loose hitting the heads of the transmission bolts. Yours is the worst busted up one I've seen. Interestingly yours appears to be cast iron while all the ones on my truck are pot metal.
From the Chevy parts book it was used over wide period 38-4? with the 4 speed transmission with open drive shaft. All of the non-CMP ones I have seen have the speedometer drive in them. But that doesn't cause a problem you will just need to plug the speedo drive and bearing holes. In fact the transmission in my C60L which is a `41 had the complete speedometer drive assembly in the retainer.
If you can not find one on a junk transmission. You might try Obsolete Chevrolet Parts
http://www.obschevy.com/ I've had good luck find parts through them, I check on line to see if they had it but didn't see it listed, but they have had other stuff I've needed that was not listed or once I described it they had another part that would fit or interchange. May take sending them a picture of your part.
Cheers Phil