I really like your engine project there, Do keep us informed of your progress and take lots of pictures. I do think it is really great that you are doing it. I think it is the ultimate form of the hobby to make your own engine, and build the plane to fly it in too.

I think the young people forget that we didn't have computers until relatively recently. But way back in the early days of model airplane flying people had to make their own engines and airplanes too. If you wanted a model airplane engine, you either made it yourself, or found someone to make it for you. They didn't have CNC machines either. It was all done using lathes and milling machines manually. Mass production actually was around long before computers came along. They used to make huge number of all sorts of machined parts without CNC machines many years ago. Now then some model engine companies used to sell casting sets to help a modeller make their engines at the time. Other companies would only sell the plans to make a engine though.

Of course the ultimate was those few homemade engines that had hand filed crankcases. There were even some guys who made engines and after machining the crankcase, they bead blasted or sand blasted the crankcase to give it a look as though it was made from a casting.