Didn't Heritage Square operate another loco that was
built by Ken Scheer of Arvada in their last years of
operation?
A gas motor/hydraulic with 4 wheels that looked like a
small modern yard engine. I saw it in his Arvada garage
once after it was built and think it was sold to the Heritage
Square RR operation at some point. I declined a chance
to run the engine out of Ken's garage onto a piece of snap
track onto the driveway and back inside.
Ken Scheer later told me they added too much weight to
the loco for increased traction over its' design limits that
caused problems. I think it was one of the last power units
operated at Heritage Square.
Sorry no photo, a forest fire toasted my current house
in 2008 and most photos/slides were damaged.