To be precice the Sport Quattro S1 and E2 were different Evolution versions of the homologation car. The S1 is the one that looks like the road version, the E2 is the car that looks like a steam train. The character was changed from "S" to "E" because FIA insisted on the nomenclature "E#" to be applied from 1985 on, for instance there were E2 models of the 037 and the 205 T16 as well.
I'd love to see a classic Porsche 911 added to the game. Something like a 2.7 RS with the engine on / behind the rear axle should make for some unique driving.
There's the FZ50 with the RR layout. You can alter engine displacement and vehicle weight with via tweak so even the tyres stay pretty big it should come close to a 911.