Oh dear, unfortunately I don't have a copy of "Excelsior the Lost Pioneer". Here's my version:
From what I can see, pre-1920 there was a bit of two-stroke action at Excelsior, starting with an announcement in October 1914 when the firm "practically decided to make a further edition to their range of models, in the shape of a 2 1/2 h.p. two-stroke mount." Pretty sure that all models before this were four-strokes: their own big singles (not sure if Condor made these, or if Excelsior sold them to others as Condor) or JAP twins. The 1915 two-stroke was a 2 3/4 h.p. Peco-engined thing, Albion 2-speed with all chain drive and a flat tank. There was also a ladies model, with the tank cut down for a step-through bit to the rear, with belt drive. The 2 3/4 (350 cc) was sold through 1915 and 1916, when it was joined by a 2 1/4 Peco option - belt drive, either direct of with 2 speed albion - during 1916, see below. No real sales to the public by 1917, so the numbers were likely very small.
In March 1919 the first post war Excelsior was announced, Villiers-powered with Albion 2-speed and belt drive. End of 1919 the 1920 lightweight models were announced with sloping tanks, as posted high up.
I wonder does Mr Liversidge agree?
ABout gearboxes - mostly Albion from what I can see, but some 1920 models (eg the 2 3/4 JAP) were shown with the 2-speed + clutch Burman so it was definitely used. I like the bike in the auction... I suspect it's pretty original.
Cheers
Leon