McGaughys does have lug conversion kit as that will go to a 5x4.75" bolt pattern. THey also have 5x5 as well, which is a lot more common for these trucks, and the typical bolt pattern for GM 5 lug trucks.
I would suggest doing a swap conversion and switching to 5x5, then using a 5x5 / 5x4.75 adapter to get the C5 wheels to fit. If for some reason you want to switch or come across wheels later, you have the traditional 5x5 pattern.
http://www.azproperformance.com/67-7...kes-McGaughys/