I have a 99 ACR. Headroom is plentiful; leg room is a different matter. I'm 6'1" and have long legs (33" inseam). My left leg touches the headlight switch even with the seat all the back.
This is really insignificant when you consider the outrageous pleasure this car brings. I've owned 11 Vettes, loved every one (especially the 94 ZR-1), but there's just no comparison. The Viper is a totally and unbelievably awesome car.
Sell the Vet, buy a Viper, you'll be glad you did ......