I'll bet not too many layouts have a guy sitting on
a chair next to the yard throat, ready to throw that
switch...

http://tbn0.google.com/hosted/images/c?q=63aa8efb7477cb32_large

It's a 1942 view of an SP yard -- note the three PRR
box cars on the far track, and the 50' single sheathed
box car.

It is a "slip-switch" he's manually operating. Not the usual
arrangement for a yard throat.
A nice find Tim.
Bob Witt