Unknown Differential

Would anyone venture a guess as to what this differential came off of? It's on a homemade trailer I bought and the wheel bearings are going out and I was going to pull the axles but found this. It looks like a cover over the spider gear pin and the pin lock is a screw head instead of a bolt head. I'm trying to figure out how to disassemble it.

Looks like GM, get the numbers off the ring gear and post them, should be a casting number or id numbers on the housing also.

Thanks MAX, I'll look and see what I can find.