I think 1969 was the last year for the 6 bolt lug pattern for the old chevy half ton trucks.
I'm pretty sure the '73-'87 were five lug wheels in half ton, except for the 4x4 trucks which are designated as K models. The K models retained the same 6 lug pattern as the earlier trucks. I've read of guys using the later model 4x4 wheels on their older trucks.
So, if you want to use the rallys, you need to look for 1967-1969 model in 6 lug.
-W
Actually, it was 1970 for 2wd 1/2 tons. The bolt pattern went to 5x5 in '71 with the introduction of disk brakes. 4x4 models stayed with 6 lug. The 4x4 Rallye, introduced in '73 on the Blazer 4x4, will bolt up fine. There was also a 5 lug Rallye, used mostly on vans. It was a 7" rim.
The only Rallye wheel used befor then was the Corvette Rallye, used from '67-'82, with a 14' version available on Chevelle, Camaro, and Nova from '67-'73/74. That one has a 5x4.75 bolt circle.
