Didn't you just post this same question in another post? Short of what Kin posted, there are really no number/letter markings that are of much help! Did you check out any of the engine ID links? As has already been stated almost all of these engines have been rebuilt numerous times and removable parts such as heads get shuffled in the process. Same goes for the internal parts as well! If your interested in dating the block (and that is just to a year range, not a specific year) check out the dating links.