Here's an idea, then. Ford Scorpio Cosworth. Comes with a quad cam V6 engine that has a reasonable reputation for reliability ignoring the chain stretching / guides that can kill it in day to day use.
Tough auto box and rear wheel drive, and lardy as all get up until you strip out the bits you don't need, seats, air con, etc. Plastic windows and drill holes to cover them in adhesive plastic in the bodywork to lighten it. As standard, pretty decent suspension. Rip out the cat to replace with a through pipe, and probably a few tweaks to the ECU sensors to adjust the mixture to suit (with the cat and sensors out, it'll run in open loop, which I think is based on the measured air flow and that can be adjusted by a pot.)
It's a reasonably quick car despite eating all the pies, so should be rapid enough even before you fit the nitrous. There's also a slower, older 12 valver with the old block. If nitrous doesn't require revs, the pushrod designed block is pretty much bulletproof. But it's not a quick car to begin with, the 12 valve v6.