Root's Engine - Model Steam Engine

based on drawings for a working demonstration of a Root's steam engine. I'm not sure exactly how the crank will turn out, but different production methods should be able to be used to reproduce this model once completed.
the models are "drilled" but not tapped.

The OpenSCAD source is included.

sizes from the drawings are:
Cover to Valve cover setscrews, tap #4-40x 0.19" deep TYP x 8
Exhaust ports, tap .25-28 NF x 0.25" deep TYP x 2
Pressure port, tap .25-28 NF x 0.25" deep TYP x 1