Most kits come with a plug socket, but they're absolute c r a p.
A B5HS or B6HS are still the best plug choice for these engines.
If you have to grind the fins a bit to use a decent plug socket, so be it, I reckon.
Throw away those (rubbish) stock plugs.
Pablo, thanks for your help with my studs. Also, love the slimline air filters. They make the stock ones look like rubbish.
Used one of your metal exhaust gaskets, too.
First test ride with billet head, 3L tank, Sick Bike Parts air filter, 'O' ringed alloy inlet, Mountain Mirrycle mirror and VELO recreational seat tomorrow. (Done 370km, so I'll go from 16:1 to 20:1 oil, too, with 8ml/litre octane booster as before to suit the hi-comp head.)
Should be fun.
... Steve