Actually, in '98 there were two heads-up classes. "Pro" and "Stock." Pro was anything goes (I think there were 4 Pro trucks, the black truck that won - Robert Najarian, I believe? -, Jason Brown running low 10s at that point, Norman Briggs running 11s and Ketan Desai running lower 12s), stock was stock heads, high vacuum cam, etc. The "stock" trucks were running mid 13s and that was all porting, converters, tires, and weight reduction. Someone got busted running a Sneaky Pete. Charles Callaway, Tom Throneberry, Jeff Petersen, etc were the fast runners.
In '99 the "stock" class was handicapped since the Gen 2 Lightnings had started appearing. In '01 (I think, I was in CA then) both classes were handicapped.
We've actually got three classes (ignoring True Street for the moment), a "slow bracket", a "fast bracket", and a heads-up. So, they're basically like the current WFC classes except we also have a heads-up class.