Thank you Vic Venters,
I'm currently searching local sources for your book.
I received the following reply from Graham Greener early this morning. He writes this about my shotgun:
" W W Greener gun no. 39135 was started on 20th April 1891 and finished on 9th October the same year. It is a double barrel sporting shotgun a G2 model, 12 bore with 30 inch barrels. It has a Facile Princeps action with self-acting ejectors invented in 1881. It was shipped to our establishment in New York so we do not have the details of the first owner. Stock dimensions when made were 2-3/4 by 1-5/8 by 14-1/4 inches, full pistol hand. The gun cost 35 guineas when sold (36.75 in todays money)." ..... "the gun is genuine, the trade label in the case is a forgery."
-Graham Greener
I am hopeful that Josef Just, Ferlach, Austria, will provide additional information about the barrel modification, and/or other history about this fine shotgun.
Everyone keep your fingers crossed.