Unless you do have a little extra "breath" on your '68, I'd recommend leaving most cars alone. You'd be surprised / embarrassed by what will legimately "smoke" our beloved car on the street.
Get on a track and get some experience under your belt, and you will find that those machines which ate you for lunch stop light to stop light may just have to enjoy a little crow on a course.
Our cars weren't meant to be drag racers. Not many, if any, Porsches were designed to be street light warriors.
Besides Bob- who looked better? You in the 968 or the punk in the Civic?! Like Fernando said, "you know dahlings, it is better to look good than to feel good!"