fxo black plastic bottom magazines

[DonVoigt]

Top pin looked like it was "flared", maybe the edge ground off- if you can push it out it is a good sign it has been changed.

If the mag base is bakelite, the hot pin test will do for it also. Heat a pin or straightened paper clip and press it into the base in an area that won't show- if it smokes but does not melt it is "bakelite"
a registered trademark for a phenolic resin compound.

FXO bases are brittle, and tough to get the pin out without cracking the base; I doubt you will find a good original.

Your picture of the removed base shows a typical crack and chip. Original or not ?
Test it with a hot pin.

I'd just buy another mag if you must have an original base.