Quote:

I looked at mine and I "think" it might have a small nub like in the pic below the plug.

the end of the head has a machined flat with the small core plug boss,it also has a threded set screw in the machined flat,looks to be about a 1/4-20 size. not sure what thats for

I see no other markings cast into the end of the head though.

I will pull the plug to confirm it has that nub under the plug

I didnt know a 452 head also used a 13/16 plug with a flat washer either.



The earlier ones did, I think by 75-76 all the 440s came with the 5/8 peanut plugs till the end of production.

75 Duster, 451 10.87 @ 123.58 NA 97 Z28 6sp., 12.01 @ 115 on a 100 shot 71 Swinger. 360 magnum. 12.58 @ 105 78 cutlass, 469 BBC. 12.70 @ 108 on street tires. http://www.youtube.com/watch?v=Z2kqNmMfheU