[Oldsguy]

Well, the number on the heads will tell their generation and hence their flow characteristics, i.e. big blocks (455s) had letter designations like B, C, D, J, and the earlier heads flowed better, the J heads were mid seventies and made for low compression use they had little bumps inside the runners that restricted flow. Small block heads (350) had number designations like 5, 6, 6A, 6a, 7 and maybe more, and some of those flowed better than others also. Then there is the engine code itself which identifies when it was built and therefore gives you an idea of it's quality and performance capabilities as well as a clue to if the engine in your car is the same age as your car itself (numbers matching comments on some sales etc). As an example: in 1973 engines had an alphabetical prefix of ccc/ccd/cca/ccb for 100 nhp 250 cid engines,; qn/qo/qp/qq/qs/qt for 160 nhp 350 cid engines and so on and then engine suffix numbers indicating manufacture numbers but many are not available, depending on the year and model and reference you may be using. Finally there is an identifying stamp on the ends of some crankshafts that identify higher quality, you may have heard of the "N" which indicated nodular iron. Anyway, you might want to go on over to Realoldspower.com and check them out, they are true horsepower fanatics, particularly the late sixties to early seventies 350 and 455 engines, the "musclecar erra". If you post a tech question there you will definitely get some positive info. Good luck.