One question. Is the sprocket currently on the bike a 1/2" by 1/8", or a 1/2" by 3/32"? This would add to Marty's belief that it was used as a road racer with gears and brakes added. The optional drilled fork and rear brake bridge also show the bike was ridden on the road. I think you can see a mark on the down tube where a D/T shifter was bolted.
It was common for racers to like to ride and train on their track bikes, but not everyone had access to a velodrome, so many were ridden on the road. When I grew up riding my track bike, the closest velodrome was 400 miles away. Adding a rear derailer was not difficult. You just used a normal freewheel hub and added the derailer by using a normal "bolt-on" hanger. The hanger was reversed for the rear facing track drop out. A new notch was filed into the hanger for the derailer positioning screw and you were riding with gears.
The interesting thing about old track bikes is to look them over closely and see how "previous owners" used them, they were just Racers, Riden hard, Put away wet.
John