[tubman]

"AnthonyG" (and "Mart") - I am not in a position to do some actual clearance testing with these plugs. I did however take a picture of a set of "N" series plug in my unmolested Offenhauser heads as well as a regular plug in an 8BA iron head. As you can see, it looks like the stock setup is a bit more recessed than the modified setup. Given this, I would follow "Mart"'s advice and clay this set up upon assembly. I don't think there would be a problem, but you can never be sure. I hope everything works out.

"AnthonyG" - I am glad that you brought this up, as it appears to have been a continuing problem through the years. I have been reconstructing in my mind what I went through. I think I came to the right conclusion in 1961 after trying many different types of Champion plugs and seemed to have forgotten it by 1994 when I used the outboard motor "surface gap" plugs (although they worked fine). Please get back to us after you get the engine together and running so we can determine the definitive answer to what plugs to run in Offenhauser heads (it seems that Offenhauser doesn't have a clue). I don't know that the heat range (the "5" in "N5") is correct; I just used it because it is in the middle of the heat range. Also, while I believe the right size plug is mandatory, the brand is not, so you may want to try some others. In addition, from Gary's "GOSFAST" comments, I think that some plugs said to be compatible aren't.

Good luck and keep us informed.

(I have included a couple of other pictures because the difference between the "L" series and "N" series is remarkable.)