You're math is correct.
The 18x8.5 ET-6 Gunner wheels will stick out 1.25" further out when compared to the factory 16x7 +6 wheels and the inside clearance will be just over 1/4" more to the inside.
Thank you! Maybe I'll go with the 17x8 Gunner instead...but then the tires aren't E rated in the diameter I want (35")
'02 PSD X Ltd 4x4 "the new a-burbit" - Noah, 2 1/2. Corrected suspension (V-codes w/addaleaf, Ride-rite's with a Bruce inspired tank, Hellwig Anti-Sway) dvd/vcr, 35's on 18's, Airaid stage 2, Walker BTM, pyro, ported housing, DP 60 special tow, 60high, 80high, 80econo, 100 perf, doo-dads, blah blah blah. Some kind of metallic blue with tan trim.
'81 scrambler...with a various assortment of 1 ton parts.
'90 blazer with a big snow-throwing whirly thing on the front
'90 YJ with lockers and stuff (kids car)
'08 supercrew paid for by work
'13 Subaru for my bride
'77 F-150 with Rainbow stripes reserved for the Relic Run TM