Mopar made some embellished "factory blue print" information to NHRA back in the late 1960s and early 1970s, the 1970 383 motors being one of them, No stock 1970 383 motors made had anywhere close to +.005 piston tops above the decks, none of them The standard stamp steel head gaskets for the 361,383 413 and all of the 426W where all .022 thick I use to keep dozens of them in stock until you couldn't buy them anymore
Ford said that the 1968 428 Cobra Jet motors had 335 HP, just like the 1966 and 1967 390 HP had Hence the Mopar response in 1969 for the 1970 model year