Find a scrap of pegboard and mark the places where you want holes with sharpie, masking tape or whatever. Tack the pegboard into position, i.e., level front to back. Drill through the pegboard holes. Then move the pegboard to the opposite side and repeat. If your floor is reasonably level, measure up to the bottom hole and set the location. Otherwise use a level to line up the holes across from each other.

I like that idea. Any more out there. Thanks bobsmyuncle. Betsy.