Have to agree with Jeff on a couple points here -- they're Cobras -- don't simulate the races on paper nor on dynos. There really is a LOT more to ET than just HP / W. If it were that simple, any engine sitting on an engine stand will whip any Cobra any day!
Stick with drag racing, do it on a track, and let the tech folks ensure you've met the safety reqs for the track.
BTW, not familiar with that Trans-AM, but one thing the GM did right on the Camaro/Trans-Am cars is the torque-arm rear suspension. Beware on road courses!
The street tire idea is good -- but get some BFG drag radials or similar, drop the pressure really low and you may want to secure the tire to the rim with some small screws.
One more thing.... want some real hi-octane fuel? Try this, but let it be officially known that I am not condoning this...
http://www.gnttype.org/techarea/misc/octanebooster.html
Cheers,
-Neil.