Help ID this rear end

[MDPotter]

I bought this rear end on FB Marketplace and I'm pretty sure it's a 12 bolt, but I want to figure out a few details on it so I can rebuild and convert to 5 lug. I've been searching all over the forum and the internet and haven't been able to decode all of the codes. The seller thought it came out of a 70s squarebody.

Castings on the pumpkin:
-GM83
-3896839 N

Stamping on the axle tube:
-KAN
-300W91

Stampings on the ring gear:
-3819037
-9:37
-GM 2 801

Pics below.

My questions:
-Doesn't KAN mean it's a 3:55 open differential?
-Doesn't 9:37 mean it's a 4:11 gear set?
-Is there a way to tell what year and model (C10/K10/C20/K20) this rear end came out of? I want to buy the right brake parts, bearings, etc.
-What is the best deal on a set of 5-lug conversion axles?
-Can I use C10 5-lug drums off a 73-80 or do I need something different?