Here is a description of Stuart's Royal Enfield goings on - in his own words
Here
is a photo of my Enfield lightening its actually a 500 so it may be
classed as a bullet, I have removed the decompressor and twin plugged
the head, easy mod if you can cope without the decompressor . The
decompressor threads are same as the plug but you have to skim a little
of the plug, the bit between the thread and hexagon where the numbers
are stamped as this bit fits inside the head. I have used a citroen 2cv
twin outlet coil for the sparks, odd shape but the bakerlight finish
looks
apt. I
have also fitted cams out of a 350 lean burn engine as these are longer
and higher lifting a small gain but worth it, you have to modify your
casings same as if you put race cams in! last but not least fitted a 5
speed box gone two up on front sprocket and one extra steel plate in
the clutch basket to eliminate any slippage, the bike pulls really well
(for a Enfield that is) runs smooth and most of all I am quite happy
with it, got other plans for it but other thing beckon
If
you fit a 5 speed box where a 4 speed box was don’t forget the gear
lever operation is different and if you gear down when you should be
gearing up well er the picture tells its own story that why it’s a 500
not a 535 
These
are a few pictures of my special its a 1960 Enfield bullet 350 fitted
with a 500 engine temporally, front forks and 21” wheel and 18” back
wheel are from a Suzuki sp360 I am in the process of converting it to
left foot gear change right side rear brake it will have alloy mud
guards and appropriate seat when I can make my mind up (comfort or
looks) I intend to enter this in hill climbs and classic enduro. The
350 engine will be fitted when this as been breathed on a little, more
on that later, it will be running a mag hopefully if I can find a
advance/retard unit at real time money(anybody got one?) 
This
is a clutch basket I have made-up out of a Enfield primary sprocket and
a Suzuki clutch, I will have to cut and weld the cover to fit over the
basket by about half inch, this will only get fitted when engine
is in and set up, it may pay off.