What number or letter on the engine code tells two bbl from 4 barrel and the compression. I can only tell the years and engine sizes. Like my 425 is a kw code so I know its from 64 and j for 63 etc. etc...
that's what one book says and its wrong, your right sorry, there is a JR code in 1963 401 two barrel and 2I for 1962 401 two barrel and LX is for 1965 2x4. they never put a two barrel on a 425 did they.