There's really no need for a custom wheel, there are plenty of viable options in 18" that are available off the shelf. A +35mm offset will work great with most of the aftermarket disk kits out there. I mean, if there's a certain style you just NEED to have and don't mind shelling out 3x the money knock yourself out, but there's a pretty good selection of 18x8.5's, 18x9's, even 18x9.5's and 10's that will work with 255's up to 275's up front.
I run 18x9's with a +35mm offset, a dr. diff 13" cobra style disk kit and a 3mm spacer. I need the spacer because I run 9"
wide rims and 275/35/18's, with an 18x8.5" it's not as much of an issue. It would depend on the steering stops, which vary a little by manufacturer of the lower ball joints.