Hi Marco,
All 4 stroke Excelsiors of around 1930 had JAP engines with Burman gear boxes.
I suggest you contact the Vintage Motor Cycle Club Library who can provide copies of all the sales catalogues for around that period so you can see what the different models look like.
As far as spare parts lists go you will probably have to get separate lists for JAP engines and Burman gearboxes, also available from the VMCC Libray.
You can contact the Library through their website,
www.vmcc.netThe VMCC also have marque specialist in Excelsiors, plus a transfer service for tank and headstock transfers you might find it useful to join the Club.
Cheers, Bob