Im no "Expert" but ive 3 oem that have the 3 holes and ive used the lower edge to index off of and all 3 have been the same with all 3 holes in positioning.

Ive a nos unit thats not drilled for the studs on the underside or the emblem, dont know if its marked inside.

I know the ones from shaker.com have two dots (the ones ive seen) inside but they seem off in position.

To me it seems pretty simple...get an oem unit, put a peice if white copy paper and put the bottom edge on the edge of the bubble, let it contour on up and mark your holes and you will have the correct spots to mark your aftermarket bubble, since the repops are so far off as it is, this will get you a hole position thats more correct then the rest of the repop unit.

If no one can get you measurements I can post my stone age method...but it works.

Alot of good smart people on this site, but all the ass kissing