I've had one of those days where you go one step forward & two or three back.
Here are most of the parts I had found for building this engine, the new parts are outside the trays on the right.
The crankcase was assembled with the crankshaft, con-rod, piston & magneto coil plate, then came the first problem, I would normally hold the crankcase in the vice when screwing the cylinder down, unfortunately the port tube in the crankcase mounting flange prevented me from using the pieces of wood I usually fit to prevent damage from the vice jaws.
A lot of searching for something else I could use found a brass earth terminal strip, removing one of the screws allowed the tube to be protected.
Here's where things went a bit wrong, I found I couldn't get the cylinder to screw down fully, I tried several times but it kept getting stuck part way. I then thought either the crankcase or cylinder might have damaged threads, I first tried the cylinder on another crankcase and it fitted fine.
The part built engine got stripped down again & I went through the other used cylinders I had, eventually I found one that fitted, ironically it was the one that originally came with the crankcase, I had picked another because the top fin had a piece broken off.
After this I needed to clean some of the parts again, it got reassembled to the point I was at before and this time thankfully the cylinder screwed all the way down with no problems. The exhaust collector was positioned at 90 degrees and I checked a starter would fit, this is as far as I've got today.
David