While I don't remember CPHs at Hornsby, I do recall the old type rail pay buses which used to sit on the tracks leading from the turntable which was just east of No 1 platform. There was a sort of locomotive depot on tracks to the east of the yard at a lower level than the yard itself. These were 50 or 53 class used on the North Shore goods trains, and presumably as bankers on Cowan prior to electrification.
These are my Hornsby depot relevant photos http://www.ipernity.com/search/photo?opt=&q=hornsby+depot&w=290173&t=0&lic=&s=0
I also remember the reddish brown coloured paybus being parked on the turntable road. The same type as was restored in a greeny colour scheme ~5 years ago. I saw it in action at least once, it stopped in platform 4 and packets/envelopes were handed to rail employees.
Through 1965 and into '66 I went to the depot on several/many Sunday afternoons (leave my bicycle at the bottom of the embankment in George St below the depot) to watch and 'help' the driver and fireman prepare and light up the loco for the North Shore goods to run that evening. I only remember seeing 53s and 55s but not 50s.
My photos show 3 roads in the depot plus a fourth one at a higher level. I saw, once or twice, an L wagon with coal parked on this road. There was also an L wagon kept near the loco for carrying ash away. The three depot roads extended nearly to the embankment for the Bridge St bridge.
I used to have two issues of the ARHS Bulletin from, I think, 1964 one which described Hornsby as a depot for suburban locos. This may be where I can remember seeing photos of it. The other issue described Cowan Bank and the depot at Hawksbury River. This supplied the steam bank engines. I saw 46s kept there attached to bank through diesel hauled trains and steam tours.