thin cylinder wall engines: the answer is.....

HP books,,Big block mopar performane by chuck senatore,,,,,,,,,Three different 440 blocks where made,,,casting dates from mid 65 to mid 68 where the first series and had a thick wall design,,,,,next series was mid 68 through 75 where the same as the earlier blocks but has cast in ribs for strenght,,these are the most desirable,,,,,,,,the third series was from 76 to 78 these are a thin wall design but still have the strenght ribs of the previous designthese can only be bored to 30 over and still have the same bottom end strength of the others,,,,,,,,,the 400's have simular dates and characteristics as the 440's