I didn't have time to take the wheels off yesterday, but they seem to fit fine and I didn't remember seeing any evidence of rubbing when I took them off. It is extremely "tight" like I remembered though; around 1/8" (maybe less) of a gap around the front edge of the drum looking in from the hand holes. So, actual GM wheels might be slightly different and not work. FWIW, mine are Accuride 28177's. They seem to be very common (both my trucks have them), so you might try finding a couple and seeing if they work for you.
Some of my crap:
1963 C-30 flatbed dually 292/SM420
1965 C-10 LWB fleet 250/column shift 3 speed
1965 C-30 9' stepside 250/SM420/4.10 gears (my DD)
Website I made for my crap:
http://www.66submarine.com