I always think of mulligan cars as being loco hauled and really for crew transport and supply.
Speeders were much more than just for crew transport.
They did light switching,
took the "super" into the woods for an inspection,
acted as an ambulance,
or took the loggers wife's to town for shopping or brought the supplies in,
and in later years when buses took over the role of a crummy they were used by the track gang.
According to "Tall Timbers Shortlines" Oct-Nov 97 issue,
the photo shows a Gibson speeder of 1937 fitted with a V8 motor, and supplied new to the Anaconda Mining Co. lumber division.
Although this is preserved the running gear may not be original.