Yep, the frame and engine number prefixes definitely identify it as an immediate postwar Excelsior. Both frame and engine numbers match perfectly. The handchange through the slot in the tank is a definite Excelsior arrangement of the day although you have to be careful how you set the gear lever as you don't want it banging against the ends of the slot.
Its not possible to say exactly what year it is as Excelsior made this identical model from 1946 to 1949. Well, identical as they could be as the world moved back to peacetime production. Some things never came back and some things were in short supply so there can be funny little differences between production runs. I would assume from the low frame number that it is early in the run.
The number cast on the cylinder is just that. A Villiers casting pattern number for Villiers internal factory use and has nothing to do with Excelsior.
The engine is the common Villiers 9D of which many examples remain in all makes of bike. Spares are no real drama. The 9D can be assembled in a variety of ways so it looks different. For example, the standard exhaust manifolds can be fitted to face forward or backward. The carburettor can be fitted on the left or right hand side of the cylinder. It looks different but it remains standard 9D with standard parts. Buy yourself a copy of the owners manual and spare parts list from the VMCC library,
www.vmcc.net The aluminium flywheel cover you show does not fit the 9D. It is for an entirely different range of Villiers engines.
Cheers,