Rear Diff I.D.

[PuzzleTruck]

Can someone please tell me what differential I have? I believe it's from a '79 Blazer 4x4. It appears to be open, by the way it can move one wheel without the other, and what looks like a bar across the middle. Gears are 41/11 (3.73).

What is the strange little device inside? It's some kind of moving weight, like you'd find in a mechanical distributor advance. I've never seen anything like it, and web search hasn't turned anything up. I'm thinking of changing to a limited slip, due to the wear marks on the carrier from bad adjustment, and some evidence of corrosion on the teeth. If this is no big deal, can I reset the pinion and lash and continue to use it safely?

Thanks!