[pjmoreland]

I then marked the location of the mounting tabs on the frame and lowered it back down to drill the mounting holes. The chassis curves up and away from the mounting flanges toward the front, so I offset the holes to the rear so they would stay in the flat area of the chassis. I drilled the holes 1-3/16" in from the outer edges of the tank flanges. The first hole was 1-3/16" forward of the rear edge, the second was 5-3/4" and the third was 10-1/4". The diameter I used in the tank flange was 27/64", and 25/64" in the frame. I raised the tank back into position and marked the hole locations in the frame. The reason for drilling the holes tighter in the frame was to hold the mounting fasteners more accurately in position in the frame. I used some 3/8" double-ended flange fasteners that are used in 96-99 Vortec engines for the power steering pump and hoist bracket.

EDIT - The mounting studs are GM part number 12557811