do you want to stretch the tire at all or do you just want a flush tire and rim combo to meet with the line of the rear quarter?
how much room do people have on the back side of the rim tire to the closest suspension components for the stock rim w/o the spacers?
i think an 18x12 et +40 with a 315/30r18 would be ok
you’ll be almost a 1/2 inch closer to the suspension components and you’ll be 0.8 inch’s further outside toward the fender from the stock rim dimensions, which should sit pretty flush with the fender (the spacers that you said people use push the wheel out 0.6 - 0.7 inch’s closer to the fender) so 0.8 should be fine, maybe running a 305 as opposed to a 315 would give you that little extra clearence to really make it look “tucked”
call me i’ll work with ya on it to find a good size for ya
Id go with the 11’s personally. The 315 will sit nicer on it(imo) rather than a tucked look that you’ll get on a 12" rim. Plus, having more dish is always a good thing!!