You can fit 315s on a 10" wheel, but it depends on the brand. Nittos seem to run a little on the smaller side and you can fit them, but Michelin Pilot Super Sports run wide and the widest I'd recommend is a 295. Just go with the tire width recommended by the manufacturer. As far as fitting it on your Saleen, you can do it, but will need to get an adjustable panhard bar or a watts link to make sure the rear end is perfectly centered.
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