Poly engines are of three distinct designs.
The Spitfire name was applied to the Polyspherical (single rocker arm shaft) v-8 used in Chrysler cars. Refer to the Identification Section for years and displacements.
The Dodge Polyspherical (single rocker arm shafts) v-8 was used in both Dodge cars and trucks, as well as the 1955 Plymouth and the 1958 DeSoto. Refer to the Identification Section for years and displacements.
The ‘A’ series v-8 arrived in the 1956 Plymouth to replace the Dodge v-8 engine used in 1955.
‘A’ series displacements: 277-301-303-313-318-326.
The Plymouth 301 is NOT the same as the 1955 Chrysler 301 engine; they are completely different engines.