Instead of using spark plugs that fit the 13/16" spark plug socket, you will now use the one that fit the 5/8" spark plug socket. The AC R45S seems to be a good guess.

There are other types of R45's that had huge differnce in electrode lenght, causing question as to whether or not the longer electode plugs would be long enough to cause interface problem with the piston. On the other side of the coin, are the short ones too short and the longer ones would give a better spark?

I asked about the differenc in electrode, but no one knows the answer. Without having a head off to see where the plug sits, I went with the R45S to be on the safe side.

Here's something to consider on intake selection. The aftemarket one is lighter; I think by about 35 lbs. The fg f-body is a lousy design, and any weight reduction in the front is a vast improvment to offset this defective design.