If you go to DAVES BIG BRAKES
OLD website, (see below) he has a template you can print, cut out and place in the wheel to see if 18 in. wheels will fit over SRT calipers.
Gen 2 guys use this template when upgrading gen 2 brakes to SRT calipers to check wheel clearance.
This is from DBB's website;
Caliper to wheel clearance
You must be registered for see images
"A" is the caliper to wheel clearance needed 1.4" min
"C" is 7.75" arc for SRT Calipers
"C" is 6.75" arc for 13" Rotors &Calipers