The 1955 300 motors are the only stock Chrysler passenger car motors that I know of that had hardened seats in them from the factory.
I believe all the H.D. truck and industrial 354 C.I. Firepower type Hemi motors that had 1/2 inch valve stems in them had hardened seats in them along with sodium filled exhaust valve stems
I'm not sure if Dodge used any 331 C.I. H.D. motors or if Chrysler even offered them in that size C.I. in the H.D Dodge trucks
All the 1954 Chrysler passenger car 331 C.I. motors I've seen didn't have the extended bell housing on them like the 1951 to 1953 Chrysler 331 C.I. motors had, which was about 5 1954 motors
As far as making that motor a good cruiser that is what Chrysler engineers design those motors for, not racing
I loved the 1955 Chryselr New Yorker motor I had in my first real hot rod, a 1934 Ford pick up that had been chop and channel with a custom made sheet metal bed on the stock 1934 frame with the early ford drive train in it back in the mid 1960s
I broke a lot of stock Ford drive train parts with that truck once I put a set of 8.20x15 inch 7 inch wide Casler cheater slicks on it