The 3 Rotor 20B is readily available. The drag race guys put big turbos on them and do some incredible times. Several Aussie built ones from the likes of Dyson and PAC performance are running 7 second quaters.
I often thought one in a Cobra would be pretty cool but it's just a shame about the noise. You kind of expect that V8 rumble rather than the rotary howl.
Years ago I had a series 1 RX7 with a 13B stuffed in it. Great fun car.
You will probably get a lot of anti comments with this combination but who cares, build it how you want. We stuff all kinds of motors into them down here.
Cheers