I have recently finished an engine loosely based on Jan Ridders opposed twin 4 cycle engine. I say loosely since I used the concept and converted it to decimal inches and modified it to be a 4 piston 2 cylinder on my next version.
I also am not the machinist that Jan Ridders is since I never got his design for a check valve to seal and went to an atmospheric intake valve.
I also "screwed up" the cylinder and misplaced the intake hole on the bottom side. I used gears rather than timing belts for the exhaust shaft just cause I have to be different.
I had a hard time getting it to run. I think because the exhaust shaft wasn't sealing well enough to hold compression. I had to lap a new shaft into the exhaust housing to get it to seal and used castor oil in the methanol to gunk up all the clearances.
As you can tell, cosmetics are not my big thing. Once I get an engine to run it goes on the shelf so I can start a new project.
My next project is a single cylinder loosely based on Jerry Howell's V-twin except my version will have an overhead cam and be driven by a cog timing belt. Hopefully the pictures will appear since this is new to me.