Drilling chassis bolt holes in the cabinet

[Noel Grassy]

I didn't see anyone mention using just the bottom cover plate as the
template for the holes. That's of course using the "setback" requirements for the xfmrs as already posted.
After finding the locations inside the cab a trisquare can be used to transfer these locations to the outside.
Bonus! If you're using 1/4 x 20 screws, their washers have enough edge
diameter to cover 1/8" (0.125 ins.) of "slop" if you needed to oval your cab holes to line everything up for final fastening.