Hello Jeffery,
If I were you, I would be looking at a sideport design. OK not much good for stunt, but it does have the virtue of simplicity. The shaft is simple turning without the complication of rotary intake, everything else is relatively simple, providing you have a case casting. I have not yet made an engine from scratch, but I have made pistons cylinders con rods and heads as repair jobs. Shafts have always been a problem psychologically, but I needed one to restore an Alag X3 diesel and was helped a great deal by David Owen of Motor Boys fame. Hardening parts is my next project and was considering making a carburising (spelling?) furnace as a project!
You will probably find that you get carried away making fixtures and fittings to the detriment of engine making. My lathe is away for overhaul right now, so I can't get diverted from building. Perhaps a good thing!
Best of luck,
Andrew.