8 3/4 identification

I just picked up a third member today, really good price and it's in great shape (so I think anyways) spins real nice, and is nice and clean. 4.10 gears and a sure grip, come type I think as I can see the springs?

My question is the case, I believe it's a 742 case, but I don't find the casting number anywhere. The number is 1634983. It's definitely a 3 at the end, not a 5, that's what's confusing me. Here's a picture to confirm lol.