All,
Plans for most of the two foot gauge equipment in the US has been drawn and released by John Derr. I do not know who has the current rights to these drawings and who is selling them. However, I was able to pick up an almost complete on eBay. I would post the drawing here, but it is subject to copyright which prevents that option. Photos of the engine are in virtually every book about the Sandy River and its subsequent lines. The drawings available from Derr are exterior details and do not show the tubes and piping of the interior of the boiler mechanism. They might not be suitable if you are attempting to construct a live steam locomotive.
For Sandy River locomotive 10 the Derr drawing is numbered "SR&RL-4". It is to the scale of 1/4" per foot and was produced in late March 1972.
The Derr drawings include a majority of the rolling stock and motive power of the various Maine lines. Some structure drawings are also available. Good luck in your quest.
Ken Kneisley
In a world without walls and fences, who needs Windows and Gates