Tain't an Excelsior, definitely a Wolf. That odd exhaust system is a dead giveaway.
Wolf pictures are easily found but you have to look in books and magazines, not on the 'net. Once upon a time The Classic Motorcycle did a reprint of the 1938 Motorcycle Show. It has a very clear drawing showing your type of exhaust system on theModel WA10 Wolf. There are Wolf pictures in Roy Bacons "British Bikes of the 30's. Every year throughout the 30's when Wolf announced their next years models both weeklies, The Motor Cycle and MotorCycling would show at least one picture of the range.
These magazines are kept by the VMCC and Beaulieu plus the VMCC probably have the odd sales brochure or catalogue for Wolf. The VMCC Library is on line and is easy to look up.
Wolf were very much on the fringe of motorcycling and not high profile but they were about for a long time and were well known. Info is plentiful.
Cheers, Bob