Dude, how can you imagine a stock stroke Poly 318 motor making over 300 HP, let alone 400
I've own and driven several early poly motor powered cars including my first Dodge, a 1959 Coronet 2 door hardtop with the one year only 326 C.I. two barrel single exhaust 235 HP rated motor. I traded that intake and carb to a friend who parents had a 318 powered 1959 Plymouth wagon sitting in their driveway collecting dust with a 4 barrel intake and carb, I put dual exhaust on it later but it was still not very powerful
My first Chrysler 331 C.I. Firepower Hemi would eat its lunch in a much heavier car That stock 1955 motor was factory rated at 250 HP
My last 392 C.I. powered 1957 300 C car was rated at either 350 or maybe it was rated at 360 HP in 1957 with the small Carter WCFB,CRS now. The 1958 300 motors with the larger AFB was rated at 375 HP, I think now. I'm not sure about the fuel injected 1958 300 D motors on their factory power rating