I can only speak from memory on this subject as I had no personel experience of taking part at this discipline. I rode at many track meetings in the south of England in the 1950's and can remember the event as part of the days programme. It always appeared to be specialist activity and very brave effort by these riders.I do remember some riders taking part in other events on the same day and use the same track machine for this purpose. In preparation for the paced event they did reverse their forks and replaced the front 27" wheel with the smaller "26" to allow for the necessary clearance required . Ofcourse all this was done to allow the rider a closer contact with the pacer whether it be tandem or motor driven vehicle.
Having said all that there may have been special bikes manufactured at some time although I was'nt aware of it at the time. At this time of certain financial restraint following the WW2 years many club folk could only afford one bike and many riders like myself chose from the many quality road/path models of the era. In the main the riders at that time were only the track rider, with a mixture of road timetrialists who would seek to ride track events as way of something different to take part in. The mention in the photograph of that great character Don McKellow does bring back memories, many feared his domination of the London track racing. There will never be the likes of him ever again ,he gave so much to the sport in the many years at the top which seemed to have lasted for ever!
Doug Smith
North Dorset
UK