This is information that I gathered while considering putting in a Pontiac OHC inline 6 into my 54 Pontiac.
Unfortunately, I chose to go the SBC route which I truly regret now. I should of stuck to my gut instinct and
put a OHC 6 in. Oh well, live and learn..
Block Casting Codes
Location: next to distributer
66-67 9787437 239 cid
68-69 9790043, 9795066, 9890043
Engine ID
Location: next to oil filler pipe on cyl head surface