:shock: If you had the huge casting, the machine work could be done with something like a Climax Portable Boring tool.
The Climax is used for things like boring Steam Loco cylinders without removing them from the engine.
You could make one, by boring a pilot hole at the rear of the chamber, then make a boring bar that slides up and down a guide rod inserted into this hole. Auto shops used to have a boring machine that bolted to the deck of an auto's engine block and could bore a single cylinder in place.
The touch hole is easy and could be drilled with a hand drill if you are carefull.
The trunions don't have to be trully finished at all, but could be smoothed with a an internal reamer(like a threading die, minus the threads). Or a horizontal mill could be made with a lathe headstock, and a section or 2 of heavy I beam to use as ways.
If we can be resourceful in where we get materials, we can also be resourceful in our machining methods. In the guidlines the windage needed for a huge-bore peice is so loose that tolerences are very forgiving anyway.
Grant