Philbert,
When I said "short chambered" I did indeed mean 16 gauge, 2-9/16" chambers. (Not modern 2-3/4" chambers)
I'm really falling in love with drillings myself so I understand the enthusiasm you must be feeling about this nice old hammer gun.
I've come to realize that the readers of these forums are not stereotypical gun collectors so take this into consideration. Most of the Internet drilling fans are hard-core reloaders that are smiling with delight when they get an old drilling in an obscure caliber. They'll hunt down dies, make brass and literally create ammunition for a gun that hasn't been fired in 100 years. That is marvelous and interesting but A.)I want no part in it for myself, and B.) Guns in obscure cartridges are worth less as collectibles.
Having said all of that, lets hope your gun's chamber cast ends up being a 8x57jr or a 9x72 where the ammo exists today for a reasonable price. Can't say I envy you trying to reload 8x58 Sauer, 8x57-360 or 11mm Collath!
Please keep this post going because I'm interested to see pictures and hear how your saga ends up with this gun. Posting pictures of the proof marks would serve to educate myself and others while probably giving you a lot more information about the gun.