Hi Nick and Jim,
I've been following your threads because I built a small flame gulper years ago that I never did get running, and while I made many changes and fixes, including some that made a difference in its reactions, never enough to get it to even turn over once on its own. I intend to return to a flame gulper when I am done with my current radial, and I'm interested in the "poppin" design, rather than go back to the one I didn't get running. Can you tell me where to get the plans for it? With regard to material, cast iron is among the easiest to scrounge, at least here in the states. A good source of fair quality cast iron in scrap is an old lawn mower engine, using the crank for shafting, and various lumps for what they are a good size for. Iron plates from weight lifting machines, or even new bar bells can be decent cast iron and useful, as well as being fairly large chunks.
It looks like you're on the way to a successful engine build, and just a few bits of work away from showing it off, Jim, looking forward to it running.
mad jack