Picture in your mind a pre war era British motorcycle and you would come up with something very much like this Sunbeam Model 9. The engine catches your eye first, but the entire machine wrapped around the 500cc single, plays the part well, right down to the "pedestrian slicer" on the front mudguard.
This particular example, previously owned by motorcycle author Harry V. Sucher, starts and runs very well and the 4 speed transmission shifts properly. The current owner indicates that while a few parts are not exactly correct, they serve well and would not likely be noticed except by Sunbeam experts or a far too fussy Concours judge.
British bikes of this era really do require proper riding attire. Strap on a full face helmet and bright colored leathers and you will be shunned. You may wish to work on your accent as well. Tell 'em your grandfather kept it in his shed after the war and saved it just for you. Of course, before you can tell those tall tales you need to own the bike which is for sale on eBay. Put on your best tweed jacket and place a winning bid.