It's a V8 of course but plugs always come in boxes of 10. I'm currently in the process of fitting a new fuel line whilst I await the Carter electronic fuel pump from the US. I did fit some new plugs a couple of year back and from memory they are 14mm.
I'll check later in case you want to sell those on Rob. Ron
I'd have to look that up Rob. But the usual way to tell a US type engine from a British one is the amount of head studs. It would have been more obvious and easier to tell if you only had to look at the plug size. Ron