They dont have to be the same size, just rolling diameter... if you have wider profile a higher profile sidewall could well work... too much pain in the ass calculating though.
Jayce, if $1000 is within your budget, check out the Falken RS-V04. Theyre meant to be fairly good, and alot of jap track cars run them. If you order tomorrow before 2pm-ish from Tempe, they can be here Friday and you can probably get Ed to fit and balance them tomorrow afternoon, or on the weekend some time.
Mmmmmmm :wassup: sticky-icky-icky ooooooooooooooo-eeeeeeeeeeeeeeeeeeee
EDIT: Thats assuming Tempe have them in stock... everytime I have talked to them after a set of RT215's, they have had these in stock (and not the RT215's) and theyre a proper R compound.