Mounting holes for sport mirrors?

[Harrison.]

My '70 had no mirrors on it when I bought it, although it appears that someone had sport mirrors on it at some point. Since I am going to have a 71-72 front fascia on it I wanted to run sport mirrors anyway, but when I removed the paint I realized the PO had plugged the original mirror holes with bondo and they are much larger than the holes that had been drilled for the sport mirrors. I am plugging those, but do they need to be the same size for the sport mirrors? I ordered new mirrors from brothers and they have a backing plate and some small stainless screws so it doesn't look like I need to have bigger holes, but I wanted to make sure I'm not missing something. I'd like to drill any holes BEFORE going to paint.