For maximum grip and a tyre that will fit at 2-3 deg of camber on a 2-series I would use a Pirelli DM (medium compound) slick. I’ve used this tyre on my Caterham and found it to be superior to the Hoosier full radial slick, which is a bit higher grip than the R7. They are difficult to find in North America, but Frisby Tire have them in 245/645-18 DM size (closer to 255 wide on a 9” rim, but on an 18x8” rim should be close to 245 wide). Diameter wise they are slightly larger than a 245/35-18, but less than 245/40-18:
https://shop.frisbyracetire.com/prod...4&categoryId=2