From 30 years as a shade tree auto tinker, my plugs of choice has been Autolite,and NGKs,, Bosch Super 's work good for me too.I use Champian in my Briggs& Statton engines cause I can't find anything else.
Scooterbob is the Autolite 4063 the way to go in a 500cc iron barrel? Say hi to Big Bill Eng for me in Beijingabe
So with the autolite, champion etc for plugs, are there different sizes to them that match up to the NGK plugs? I use the b8es but don't know if the other other makers have similar sizing or what? My little RE is a bit touchy around plugs so anything that would be even a bit helpful IE: get me to at least 150 miles before having to change plugs would be nice. I'm carrying about 4 plugs on me (really TD is the one with the plugs in his sidecar). Gromit
The old 4063 is a good choice - so is the 63 if you want a non-resistor (gasp!) plug .... I'll sure pass the word along to Bill ..... I owe him an email anyway! Hahaha!!
I have to check other parts sources..Auto Zone doesn't have or can't get the Iridium.
This site even lists the Royal Enfield 500 as a application for the "4063" not too many sites list our bikes.