Widest Front wheel with alterkation

Wracks71 is running 18x9's with 275/35/18's on the front of his Duster with his RMS Alterkation. He said they're from American Muscle, which lists the specs on their FR500 replica's as 18x9's with a +30mm offset, which is a 6.2" backspace. He also said he's running wilwoods on his RMS Alterkation, although I don't know which ones and different brake packages can change the track width a little bit.

His specs are listed at this Hot rod mag article, scroll most of the way down the page. It doesn't list his backspacing though. http://www.hotrod.com/cars/featured/1312-2013-muscle-car-of-the-year/