Got my owner's manual right here
The 350 was an available option. Standard in the Fury was a 318 with dual 4 barrels, 9.25:1 compression, and a performance cam.
Standard equipment in the '58 Plymouth was the 318 Polysphere V8 with a 2 bbl carb, not to be confused with the later 318. That's what my Savoy has.
The "Powerflow" flat head six was a 230, and it was optional....