Is it possible to reverse intake/exhaust through use of a valve to reverse rotation for short term uses such as docking, etc??? Seems that I read of it somewhere as a possibility.  Does anyone know of this?  Possible sources or drawings available??

the wilesco D48 twin uses something like this...

You can do that on wobblers.  Reversing exhaust and intake ports will reverse the engine.  It works better on double acting engines and even better on twin wobblers.

Hi all
The wilesco D48 twin is a piston valve engine, Reversing the inlet and exhaust will only work with piston valves and oscillators (wobblers), if you reverse the two with slide valves it will lift the valve off its face, and the steam will rush out the exhaust.
Regards,
Gerald

Thanks Guys for very helpful info, esp the drawing download.  
Harvey in NC