I'm answering this strictly from memory, but 1: Definitely sheet metal screws and 2: There is actually two layers of metal separated by about 1/8", the tail edge of a crimped & spot welded joint. With the capping removed, you can repair the top hole if it's become oversized thru the years but I don't believe you can get at the bottom hole. The designers certainly didn't look 45+ years ahead when they opted to eliminate the wood base. Lift-the-dot sheet metal screws have always been #8 (only) so getting a #10 to compensate for the worn out hole is out of the question. My 3A was already painted when I discovered the oversized holes. I tried several "fixes" but nothing that I was completely satisfied with. The closest I came is a product called "Mr Grip screw hole repair" made by Woodmate Corperation. Designed for wood but works well on metal.
Hope this helps.
FRank (My memory isn't what it used to be, & also, My memory isn't what used to be.)