I would also like to hear about the "dash" number after the engine size. Pretty much all of the Mopar engines have them, "318-8" "360-6" etc.
I will tell you what I have heard it was and I am not saying this "is" what is or I'm not discounting it either because I don't know what it is and was hoping that someone can tell us.
I heard that it is the quality of the casting as far a accuracy like core shift, etc. the lower the number means the better the block. Well, that's what I heard when I started buying Mopars.