Where Do I Fill This Thing?

[magwakeenercew2jh]

Unfortunately, I put the bed back on before I looked around at the pumpkin and differential case for a filler hole. P/O/ pal went with this ribbed cover.
I can see the drain. I have a gallon of new lube for the differential that has a pump on it (altho I'm not sure how much the rear end holds).

I'd like to save at least a little dirt in the eyes by asking you folks before I crawl under there tomorrow.

Also, can I get some idea of the (original) rear end gear ratio from the casting on the case?

Thanks.