The best starting point might be a trip to the Vintage Motor Cycle Club Library at their Burton on Trent HQ. They have bound copies of 'Motor Cycle' and 'Motor Cycling' from the year dot and also lots of other paperwork.
They're ever so friendly and membership is not required. In fact, in contrast to many archives, they actually give the impression that they're pleased to share information.
I'm sure you'll find some useful photographs there (but don't blame me if you lose a day !