Is it possible??

[Freedom_Fighter]

How about with a complete fender roll in the rear would 255-35/40-18 clear on the stock rims?

[Yeller Jakett]

Prolly don't need a fender roll. GoatChs has 265s on stock 18" Monaro wheels with no rubbing. Right, GoatChs?
http://ls1gto.com/forums/showthread.php?t=45167&page=4
Scroll towards the bottom...

[ls6gto]

If you are going to roll the rear fenders, slap on some 275/35/18's - nevermind, I dunno if those would fit the stockers.