DavidNJ

Your issue is over width vs. offset. 17x10+50 I think work with no flares and minimal fender rolling. Common in NASA TT5. However, those guys have to get the tire through a 266mm width template and typically use 245/35-18 I believe.

Every car will be a bit different depending on ride height, camber, offset, and tire size. It is a bit of work, but you may want to pull a shock on each end, disconnect the anti-roll bar, construct a template of the cross-section of the tire and wheel with some maximum positive offset, and the try it moving the hub up and down with a jack, turning the front wheel through its travel. A spacer can simulate different offsets.

Street fitments often use modest sizes and less positive offset. For looks, even a 245 can look wide by itself. Obviously, a 315 is wider!

A big question: what will the car be used for and what brand/model of tires are you considering. The really big stuff is generally in race tires (i.e. tw60 slicks). Some come in tw200 tires targeting racing classes that spec a tw number. Autocross street and the popular STR class fall into the category.

In real street tires, you may find 255/35-18 or 265/35-18 is the widest available that fit the S2000. 255/40-17 is the common size used square in STR and in the rear in Street autocross classes.

How much power are you planning to pump out of the LS? There are a lot of forced induction S2000s running big power numbers with a wide powerband made possible by the ability to increase displacement and rev to high numbers. Many use E85 or oxygenated race fuels to get really big numbers. One forum member was interviewed for a video on his 960hp street driven turbo S2000...stock displacement. He just posted the link the video this week.