3500 rotor swap 71 to 77 ????

[old Chevy guy]

Ive been trying to get the rotors to put dual wheel rims on the front of my truck for some time. Its only a 71 c 20 but its heavy duty and I have swapped over to rear duals long ago. It has a Stake body dump on it. Ive tried to buy several rotors off trucks being parted but could never work out the shipping with the sellers. Today I was at the local junkyard and there was a 77 c 30 in the pile with practically new rotors on it. Does anybody know if the 77 3500 uses the same rotor as the 71 if it was a 3500 or a C30. I tried to look it up on some part sites but I cant find the rotor listed for the 71 with a dual option. However its the same part for 77 and 71 with single wheels if that means anything. Im sure I could buy them for a song but it wont do any good if its not the right part. It wont be there long before it goes to the shreader either.