Both Skateballs I've seen have factory mylar. I would be VERY hesitant to remove factory mylar on an 80's Bally. I'd like to see pictures of the playfield (if possible).

I've used the "hair dryer" trick with great success over the years. You will need shellite or white spirits to remove the residue. For more info and heaps of advice - Just do a search on "mylar" or "contact".