Ok, this is why I don't trust mechanics either. (don't need to start a rant, but this once again proves my point) There are WAY too many idiots working in the automotive industry. I've got the PAPER parts manual from '85-88, and it's group 9.000, page 9-4.
The part numbers for the actual steel pieces riveted to the frame are as follows. Numbers start under the cab front, NOT including the core support mounts:
Mount 1: 14040692
Mount 2: 14029286
Mount 3: 6274179 (LH) and 326418 (RH)
Mount 4 there really isn't any replacement "mount" just the piece the bumper bolts to, upper and lower "cushion", a spacer, a bolt, and a nut.
I kind of doubt all those part numbers are still good, however, given the incompetance of your local dealer, I would STRONGLY suggest you take your business elsewhere, such as
www.gmpartsdirect.com
They kill you with S&H, but if your dealer charges you prices inversely proportional to their intelligence (like mine) you will either come out even, or a bit ahead.