Help with autocross tires on my 72 Nova

[YENKO/SS]

Heres my HUGE problem. Im currently running Nitto450 275/50-17 & 225/50-17 tires. This car has evolved into a weekend racer and these tires SUCK. I have looked at Direzza II, Hankook Ventus R, BFG Rivals which all have a 200 treadwear rating, ( required at most tracks) and they dont offer anything close to a 275/50-17. The dimensions on this tire is 27.8" tall and 11" wide. I can match the 225/50-17 pretty easy.
Ive included a pic of the car to give an example how critical the tire radius is to the look of the car, so a smaller tire is not an option. A newer set of 18" rims would help as it would open the door to bigger tires, but it would set me back another $1000.00. Just not in the budget. Appreciate any help or recommendations.

[Buick Grand National Guy]

Go ahead and bite bullet and go to 18" wheels! Don't look back! Cool car!
Conrad