Been having similar problem getting a new dash pad to fit on my '65 (dash pad is for a '66). In my case, the pad just won't slip far enough onto the steel dash for the screw holes to line up along the bottom. AND....my speaker grill screw holes don't correspond to the ones in the dash...not even close. Like you, the pad was put on by PO, and I don't know the maker (but has a Ford logo embossed on the inside).
If you figure out how to fix yours...let me know...and I'll so the same from here! GOOD LUCK!!