It's an 8j rim, rather than a 7.5j - so 215 or 225 will be fine.
You can easily fit 235s on an 8j, but going much wider, you'll want to be dropping to a 40 to account for the extra rolling radius, There's also more potential for rub/poke as I think the racer wheels are a different offset too.
My track tyres are 225/45/17 and are fine, cheaper and easier to find too.