Greg,
Have never visited the Sugar Pine, but from what I have heard it is an ex-WSL engine. I was thinking the other day that I have lost track of where the WSL engines have gone. Maybe someone here can provide a list of current whereabouts.
I believe the Sugar Pine track was laid at least partly on the grade of an old loggging line, but it was not WSL. WSL was north of Yosemite, the Sugar Pine operation is south.
Most people don't realize how heavily parts Yosemite was logged before it became a National Park. The original park was much smaller, and was extened into the logged over areas much later. Lots of old logging railroad grades within what is now the park. But that was all standard gauge so we can't talk about it here.
John