Thank you again. You mention "gears". I will have many questions on the gears in another thread when I reach that point. I have never made gears; but I desire to learn how to do so.Don't worry too much about it, just stick to the plan and you'll be fine.
I can tell you: If the cylinder and piston on my engine are ok, I am sure that more than 90% of my engine will run, the other parts are just surface treatment on the outside such as valves, gears .... much simpler than making the cylinder. So be confident.
Just looking at the picture, it is not too difficult to think that you will succeed !!