Being a welder, I would probably modify the crossmember to meet the needs of the Gear Venders unit to use available mounts.

It sounds to me like even the lower mounts will be too high. So some kind of modification may still be required. If modification is still going to be required, why not just modify the crossmember to use the available mounts, and leave the OEM mounts for the guys doing numbers restorations?

Lowering the plate the bottom stud bolts to even a 1/2", wouldn't be a big issue at all if you have the clearance at the top. If it needs the 1/2" and there isn't clearance at the top, that can be corrected at the same time. The crossmember is only steel.