I don't have the measurements, but I do know that the holes had inserts in them to prevent the body from collapsing. You can replicate the effect by over boring the hole through the stiffeners to the size of a section of pipe. The hardware was 3/8" if I remember correctly, so you need 3/8" i.d. pipe. When you put your flat washer on, you won't see the mod. I'll pull the pictures up in the morning to see if we can come up with reference points to get things pert near close.
