Just about to start my new swap

You're on the right track with a whole car you can take parts from. The Challenger was not out when I hand fabricated a new tunnel and crossmember for my Tremec trans. Once they came out, I ALMOST ordered a new tunnel from the parts department to start over (I love factory parts), but mine had turned out real nice and I decided it wasn't worth it.

I also fabricated the floor area and mounting areas to mount SRT8 "Sport" seats into my car. Again, it would have been nice to have all the floor mounting parts from that Challenger for a more factory engineered design. You could then use the Challenger front carpet which would fit the tunnel and under seat area, then trim it at the outer edges. Mine is going to have to be all custom carpet because of the custom tunnel and flooring...