I've been through all my files, but cannot find what I'm looking for:
the plans for a small model steam engine - cylinder is horizontal and has
two elliptical holes diametrically opposite each other, channels in the
piston direct the steam alternately to each end of the cylinder. A pin in
the "drive side" of the piston engages with a coupling to convert its
motion, reciprocating and "wobbling", to rotary motion and thence to a
flywheel. I seem to remember the valving is somewhat similar to an
oscillating engine's.
Further suggestions included a twin with the output coupled by gears.

IF you recognise this description and have a copy of the plans (Pop.
Mechanics/Mech. Illust.?) I appreciate a scanned copy to:

mcgray at telus dot net (usual changes needed)

TIA,
Mike in northcentral BC