The 1" setback plates are the way to go. This eliminates driveshaft/crossmember problems. Had I known there were differences between manufacturers of the plates and how they were made, I would have suggested the ones from Trans Dapt. right off the bat. Since all the top holes are in a straight line, this would have moved the clamshell up enough to clear the casting.
As for a course of action, just notch the clamshell. They are plenty thick and strong enough even with a notch or two in them.
The A/C bracket definitely works too. It took some tweaking due to some belt chafing but it all worked out.
'93 Chevy 1500 4X4 ECLB with a '99 Silverado LQ4 6.0 and '99 Escalade 4L60E. SOLD IT!!
New toy: 2001 2500 HD 4X4 Extended Cab Long Bed
John