65 12 Bolt fill and ID

[kizer]

I'm new to all this so if I ask a dumb question its well all new.

Ok I was looking at the rear end since I've recently ripped all the wood off in the process of taken the bed off so I can prep the frame with POR-15. I decided to take a peak at the rear looking for gear ratio and whatever info I could find. On my Jeep there is a little tag on the cover bolts on the left side.

2 questions:
- Where is the Tag to identify the basics of the rear end. Gear ratio and whatever else.
- I also didn't see a fill plug on the cover so how do you fill it? On my Jeep you pull the cover to empty it and replace and open the fill plug.

I suppose you could use the vent tube looking thing on top, but that's bizarre. Also looking at the rear I'd be surprised if it was ever changed, which can not be good. I normally change my Jeep once a year since I play in literally every terrain.