I have heard of a random washer falling out and getting lost when cylinder was reconditioned...  the one I remember the machine shop used one of those heated high pressure wash cabinets like a big dishwasher for engine parts. 

I don't remember if it was this forum or the old one...  but someone also thought the washers were missing and added new ones...  a mistake discovered when they either stripped a cylinder nut or noticed there weren't many threads showing on the studs...  can't remember, it was a long time ago.

Ahh--ok, things to be careful of.

In my defense, you can't really see the pressed-in washer.
So I carefully fitted the aluminum bolts and could see that they are in place and secure the cylinder. So the washers seems to be in...

I had the same problem with my Royal Enfield, it was important that they were special aluminum washers which you should not forget. Hence the question.

Royal Enfield-- umm--its 60 years since I worked on my 350 bullet. Where I worked back then we were RE agents but don't think I ever saw one in the shop except mine. I used every new gasket set we had jn stock as I had it in bits almost weekly. It was my first motocross bike but kept throwing me off then jumping on me just to teach me a lesson haha. I Won the war & sold it to my mate.

I imagine an Enfield as a motocross is quite heavy and sluggish, but a nice experience you describe!
I converted my 500 to a chopper and after some optimisation don't really have any technical problems. But I also don't ride very much and certainly more comfortably than you did off-road. Did you have any thermal problems? I also fitted a larger oil pump, as the original one is probably quite small and can cause overheating.
If you are interested, here is a short video of mine
www.instagram.com/p/C9PbpsjIMyL/

I have now reassembled everything and was able to start it for the first time yesterday.
I also replaced the ignition (breaker contact, capacitor, ignition coil) and checked the oil pump for minimum stroke. Also replaced the diaphragm inlet. So I should have replaced all wearing parts as a precaution.
It started on the first try!
Im happy with the new paint, hope it lasts a long time without flaking off.

Here some photos of the final result. PS: After the video, I set the pilot air screw to the factory setting. This made the engine run better
imgur.com/a/Q3r83RS

I have now filled up with 1:100. How long should I take it easy on the engine before I can turn the gas tap properly?
I will retighten the cylinder head as described.