This is from a message board:
1970 GTO 455/360HP HO engine, order code L-75- block code for the automatic is YC & YA. Manual trans was code WA. The YC code was found in only 1 book (which is basically a Pontiac "bible") that I have while the YC code is listed as a 1971 455 engine. The 455 is called an HO engine in the GTO where 71 and later had both a "standard" lower HP version or the higher HP "HO" engine with the aluminum intake.
Heads are#64. Full casting number is 9799364.
I have several references to the 455 "ram air", so it may have been a package option.
455 CI Q-jet # for manual trans is 7040267 -non ram air
7040279 -with ram air
automatic trans is 7040268 -non ram air
7040278 -with ram air
Number of GTO's equipped with the 455HO YA/YC engine is listed as 2227 (241 Convertibles).
More investigation is definitely needed and I would get the PHS documents to verify the L-75 455CI option, along with the rest of the info for the car.:thumbsup:
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