Can anyone tell me what that is? Thanks.

 

OA--all it says is 3.73 "lock".

Since it's a "locking" (probably limited slip) differential and a non-9 inch ratio, and a '60 F100, I would say it's probably a Dana 44.

Does it have a removable rear cover?

Pictures and where to find id info on a Dana axle:

Axle / Differential Identification

 

Thanks for the reply. Only part i did not know was the ratio. Terry