hemi heads 1954 down 331's , 1955 301 331 these heads and blocks have one year only dowel pins , 1956 - 1958 354 392 interchange . you can fit the early 55 heads on the 56-58 with some rework . 1954 to 1955 the water jacks changed . i have several early hemi projects on going . here is the 54 331 twin fours , 54 331 ind i'm punching to 354 with algon injectors , here is a 55 poly 301 i've converted to 55 331 hemi heads , building a desoto and a chrysler for the salt racer . i've got a 354 bored n stroked to 426 on its way . and a 392 out of a drag boat , i'm not an expert , but i can help if needed .