Oh, well there IS a tunnel under the floor, and you'll need to run some pretty intelligent exhaust routing, a new splash guard on the tunnel, and the rear will be hollowed out to favor the MacPherson setups from.. like, and old Toyota or something. something narrow. The S2k rear suspension will require all new, and precision mounted, a-arms and alignment control arms. That's going to be the hail-mary here.
I've thought about it with a raised floor and a Porsche 944 transmission, or a complete out of the box solution like a Lotus 7 chassis. But then you're talking about a Lotus 7 with a CRX body on it, and the front chopped about 12 inches.