Startech has a 6.1L V8 conversion for the Crossfire. They also make kits to punch displacement up to 3.8L on the stock V6 (from 3.2L). Since Startech is owned by Brabus, you can bet that all of the stuff they sell (from styling tweaks to powertrain upgrades) will be hideously expensive.

http://www.startech.de/p13e.htm