I think WormGod's wheels are 18x8.5" with 0 offset, right Gary?
And, he has 285/60-18 tires that required trimming to fit.
Look at his gallery to get an idea of appearance.
Also,,,,use tirerack's tire search feature to see what tires fit with which wheels, what their width should be, and overall diameter.
Stock diameter is about 29.75" from what I can tell. I think they're 38mm offset too.
Wheel/tire combos I've seen recommended online usually land in the 18-20mm offset range. Past that's probably where you gotta start trimming -- especially if the diameter is bigger. Or,,,maybe their is more than one offset for that size.
Edit: I just looked up KMC Rockstar. eBay had the 1st set of 18x9 with 6 x 5.5 pattern. That auction says the offset is 35mm (not 12mm). So, they match up fairly close to the stock config. If anywhere clearance on the inside would be in question (IMO).