One thought is that there are lots of flat sixes that will swap out. However the Chryslers and Desoto sixes are longer and will not always fit. However, Dodges and Plymouths are the same externally. I picked up a nice 48 Chrysler six because the owner could not fit it into the engine bay of his Plymouth car. Check this site...........................http://www.allpar.com/mopar/flat.html