While the best option is use your car's original engine if it is exactly what you want, replacing your engine with a different one can be done with varying amounts of difficulty, depending upon your choice. The factory is a good place to start as buying a brand new engine can sometimes be competitive with the price of acquiring a rebuilding a worn engine. Mopar Performance, however, does not carry any slant six engines but slant sixes are still relatively cheap and not that hard to find.