That style of beam is actually quite easy to do. The average cast beam is not going to have the profile spot on to the nearest micron and mould misalignment will mean you end up filing the outer profile to tidy it up anyway. Fabrication is the way to go, so print out your eliptical shape and use that as a template to saw/linish/file a piece of say 3mm plate or flat stock.
Take two lenghs of flat or cut strips from sheet, mill a 3mmx 1mm slot down the middle to locate on the central web. Clamp to your 3mm web (they will bend easy enough) and silver solder into place.
Now drill for the various bosses, plunging or boring the ends to tidy up the previous work and bond or solder the bosses into place.
Now treat as a casting and do the final bores and reamed holes in the bosses.
I did look at the ME beam article last night, not too hard to do.
– Bed plate made from two layers of either aluminium or steel with an 1/8" one at the bottom to form the flange which saves a lot of cutting. Bond on the numerous hold down bolt bosses and mill the top raised features and moulding around the edge.
– Cylinder is a tube with flanges added each end and a coped block for the port face
= Column, probably do from steel round with square bits added top and bottom or you could turn from larger solid square bar
– beam as above
– Flywheel cut from billet and as it's a freelance design you could go got a more rectangular section to the spokes to save handwork
Bronze is another alternative for cylinders as it allows silver soldering if you don't want to JBweld as soldering cast iron is possible but not the easiest thing to do
As for needing CNC for beams, this engine's beam(s) was done before I had CNC, just outsourced some water jet work on the flywheel. The whole thread shows a lot of fabrication or cutting from solid that would be applicable to any other beam engine or any stationary engine come to that.