Originally Posted by Drillium Dude

Those are the inner stop plates. You should be able to slowly work them off with a flat screwdriver by lightly prying from the back - use a shop cloth to protect the paint. Strange looking plates, tho - what is the frame and what was originally mounted on it (parts-wise)?

It doesn't appear that they've been brazed to the frame bosses, so you should be okay.

DD