Thanks for the above comments; I’m eagerly looking forward to building this engine.
I got a start on cutting metal on this project today. I’ve been reviewing the drawings with various measuring devices close at hand, trying to get a feel for how to proceed. Bob Banke, in his construction notes, warns that there isn’t much room for error with these castings in that there isn’t much extra “meat” provided. Being for-warned, I thought it prudent to mill the surfaces that require a close tolerance first, and let the minor surfaces till last. With that in mind, I proceeded.
I thought I’d start with the crankcase frame. This is the base of the engine and as good a place as any to start; also the lowered numbered drawings- indicating that maybe this is the way Bob envisioned you should start.
The base of the frame casting was fairly irregular. After some thought, I decided to just mount the thing in my mill vice and attempt to get the top surfaces level. This I did with a test indicator and a few shims where needed; running the table back and forth and shimming where prudent.
The top of the main bearing surfaces were addressed first. One was fairly level; the other was cast on a slight angle. I brought these in true as shown with a surfacing tool.

The engine features an open crankcase with the cylinder casting mounted on pedestals, reminiscent of steam engines of the period. The bosses for then pedestals were brought into dimension.

Next, while everything is still square, I drilled and reamed the holes for the above mentioned pedestals.

The faces of the casting where the main bearings reside were brought into dimension.
Next I drilled the frame mount holes for the engine. I couldn’t drill these through without drilling holes in my mill vice. I chose to drill them nearly through but finish the holes later. With them started, I figured I could spot these holes accurately enough to finish them.

Not specifically called for in the drawings, but experience has shown that it’s advantageous to have the sides of the engine frame in alignment with the other frame dimensions. Keeping the center measurement I figured earlier, I removed just enough material from both sides of this frame so that either side is a parallel reference and by locating the two sides and halving the distance between I can relocate the centerline (crankshaft line) on this casting.

And by performing the above operation I was able to flip the casting over and re-align the centerline to the mill table.

The drawings called for this flange surface (where the engine mounts to a carriage) to be two inches from the top surface of the main bearing surface. Even though I removed the minimum of material to get the main bearings surfaces (1st step) true, I had barely enough mater to maintain the two inches as specified in the drawings.

The drawings called for the bottom of the engine frame to be 3/8th inch below the above flanges. After dropping the mill table the required 3/8th inch, the surfacing tool did not touch the surface. Since this is a non critical measurement, and since it’s advantageous to have a flat surface for the engine to rest upon (during construction) I just raised the mill table until I was able to remove some material from every part of the casting. This really only makes the depth around .030 inch short of the 3/8th as stated in the drawings.

The pedestals upon which the cylinder casting mounts are fastened by blind nuts on the under-side of the engine. Here I’m milling relief for the nuts. I’m just spotting these recesses over the original holes.

Time to finish drilling the engine mount holes.

Since I milled the side of the engine base in true with the other measurements, and since the bottom of the casting has been milled flat; I can just mount the engine base to a right angle plate, measure out, drill, and tap these holes for the water pump.
That should about do it for today. I’m not nearly ready to move on from this casting, still to be addressed are the cut out for the main bearings, the gears, and the bearing cap holes. Good enough progress for today though.