You can use an OS number 8. Perfect plug for you engine and very durable. I use to go through loads of plugs before, OS plugs seem to be much better.

Just about anyone sells them in the UK ie:- modelsport, gm models. Take ya pick but GM post them for free, like all their stuff delivery in UK costs zip. Dont just get one. get at least 4 or 5 and when one breaks ( usually first couple of tanks and it will) you will always have a spare. Dont be sidelined on a sunday because you have no plugs.[]