A 255/60-15 is the widest tire recommended on a 7" wide wheel. A 275/60-15 tire needs at least a 7.5" wheel per BFG.
http://www.summitracing.com/parts/BFG-17476/
BTW...hellava of a gear ratio you've got there!!! 
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2017 Camaro RS -217 cu in 365 HP w/8 speed auto
1967 Camaro SS -5.3L LS w/4L60E & 4.11 12 bolt
2019 Cadillac XT5 3.6L V6 w/310 HP & 8 speed AWD
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