IMO, using an O.S. glowplug in any Novarossi based engine is
a big mistake. The O.S. glowplugs will deform the sealing
area of the head button, then you will encounter sealing
problems if you decide to switch to another brand of glowplug.
The O.S. P3 glowplug is way too hot and very fragile to be
running in these engines. The only reason for running a plug
that hot is that it will make an out of tune engine seem like
it's dialed in. The RB and Novarossi glowplugs will outlast
any O.S. or O'donnell glow plugs made and they don't cost that
much more.
Why go the cheap route and take the chance of ruining
a piston and sleeve by dropping a glowplug coil into the
cylinder ?
Buy a quality glowplug of the proper heat range
and you'll get many gallons of trouble free performance
out of that fine engine.