It's a pretty old base, I've had a look back through some old gun digest books I have but none of the Weaver lists had the base. Yes the fitting instructions state that the bottom saddle part of the scope ring is screwed to the base so they are not detachable types. Would likely be impossible to find rings for the base now unless someone has any lying around.

If you really wanted to use the base you could mill/grind the dovetails off a suitable set of detachable rings, centre bore and countersink a hole for a mounting screw then mount them up. Don't need a recoil pin or stud on the ring saddles as the base recesses will stop ring slide.
If it were mine I would do it this way just for the heck of it but I ain't going to bid on E-Bay so it is all yours.