I run a set of 452 heads and just installed autolight 23 5/8" hex tapered seat "peanut" plug.

my 440 is from a 77 1 1/4 ton chassis motorhome.

the heads I swapped on this weekend, another 452 set got a set of the AL23 plugs as well.

but when I asked the machine shop(chebby guy)he said they are machined for the flat washer style plug but the tapered seat plug will seal.



AL23 are what was in it and the plug hole/seat look the same to me with no leaks so far.