'71s are 5 lug. It was the first year for disk brakes on Chevy trucks, they ware standard equipment. The '71s had a decal on the tailgate that was a yellow and black striped rectangle that said "Caution; Disk Brakes" on it. I remember that decal on my Dads '71 C20. GM also went to 5 lug on all 1/2 ton 2wd models, 4x4 stayed 6 lug but used disk brakes as well.
