Art, I think your idea about keeping the cars as similar as possible in nearly every respect is great. And, as stated previously, the headers are going to be an issue. For the short time that I owned a Scarab 240Z, the headers were full length and the steering rod went right through them--I don't remember the block huggers being able to fit(?!) but that may be just my memory.
If this turns out to be true, try to use a "short" header that works for the Scarab set up to keep the power levels about the same for the comparo. I know that goes without saying, but full-length vs shorty isn't exactly equivalent. In my mind, that is the biggest obstacle.
Also, you can get a number of people to drive the cars in their respective fields of expertise, and then let them comment on each set up. In other words, get a drag racer to do the drag racing; get an autocrosser to do the autocrossing, etc.
The article would be like the king of all articles as far as I'm concerned, especially if you keep it as "scientific" as possible. I rather like the idea of using the SAME car for the test. That way, there is no fudging the numbers.
Thanks for taking the time, money, and inspiration to so this.
Davy