I agree with Autolite 45's and how do 14 mm plugs fit in 18mm holes? You better take a good look at your heads.

 

I'm curious on how 14mm plugs fit in 18mm holes?

 

That is a good question, Iused JB Weld, so far so good....



















Actually, the Vic Jr. heads use 14 mm gasket type plugs, with a 3/4" reach (threads) ,,,, the ones that use a 5/8 socket.

But I would have to say it would be easier to put 14 mm plugs into an 18 mm hole than vica-versa, if I were going to try such a thing....

 

The PO said they are gt40 heads, but are the threads different than stock heads??