You can check with this member to see if his rotors are within spec for turning
http://67-72chevytrucks.com/vboard/s...d.php?t=188259
or as a last resort get some 3/4 ton rotors (yes they will work) and put these adapers on.
http://www.southwestwheel.com/mywebs...4c_1323749.htm that would be expensive but like you said these rotors are hard to come by. I looked myself this last summer and never found any and went the adapter route since I had a good set of 3/4 rotors on hand, but it looks like they had a major price increase since I did it.