1952-59 Ford how do you check/change/add fluid to this rear diff?

I see the drain on the rear at the bottom of the pumpkin in my 53 but I can't figure out where to put the fluid in. Suggestions?

 

I know on my 54 above and almost on top is the fill plug. I don't remember which one was which but one was recessed. I had to jack the car up by the rear axle, put the body on jacks and then let the rear axle down to get to it. Hope this helps.

 

I was under the car but didn't see anything. Maybe it's just hidden under the years of crud I haven't cleaned off yet. I will get under there and take another look.

 

If you look inside the p***enger floorboard. thereshould be a oval plug. If you open the plug and look at an angle you will see the fill hole.