I'm also looking into building a diesel engine like the one of mr. Find Hansen. If you carefully follow his youtube videos, he gives away some numbers. His green engine has a bore of 20 mm and a stroke of 40 mm which compresses into a head clearance (diameter 20 mm) of 1 mm and a combustion chamber of diameter 7 mm and 8 mm deep. This for sure helps in mixing the air and the fuel as there will be a lot of swirling air. This is where I put my money on for my first design.
Indeed, (almost) adiabatic compression gives much higher pressure (due to increased temperature) than compression ratio would tell you. The numbers regarding forces are enormous as Mr. Hansen also clearly points out. Hence the need for some good lubrication and a very sturdy design.
Once my engine is running, I will make a full set of drawings (with at least the critical dimensions) and make them available to any other interested person.