Thanks for your comments, fellows!
I have a few more updates on this construction.
I'm going to use castings from PM Research (a company in the States) for the inner part of the flywheels. I need to
make a couple of outer rims of steel to shrink onto the OD of these. Haven't got to that part yet.
I couldn't hardly resist using these castings. A 3.5" flywheel for $6 ain't bad.

Setup for drilling and tapping for the set screws. When I put set screws, (grub screws) against a crank shaft, as will
be done for these flywheels, I put a small lead shot in the threaded hole first. Keeps the set screw from scarring the
shaft.

Next, some squaring and boring for the top of the firebox. The engine assembly gets mounted to this piece via the
four holes in the corners.

The gaskets that go between the hot cap and the rest of the engine were cut from ceramic fiber sheet.
This stuff is available here as a substitute for asbestos. I can post the U.S. suppliers' contact info if
anyone would like it.

Cutting out the sides of the firebox, I began with a hack saw. That was taking way too long by the time
I had got one of the four needed cut out.

The remaining three were cut out on the mill. A lot faster.
Too soon old, too late smart! I eventually figure this stuff out..

After the four pieces are cut to shape, the corners are filed to a 45° bevel. Again, I did the first
couple using only the file. The rest were roughed off with the bench grinder, then cleaned up to
the proper angle with a file.

After the pieces are all filed, the bevels make for a nice fit-up.
Much to do on these yet before they can be soldered up.
That's it for now.
Thanks for looking in.
Dean