More info.

H&H got back to me. The gun was sold new in 1891 to a Mr. Dalton. It is a 500 express designed for the 3 1/4" ammo.
With a 13 3/4" pull, open hammers, extractors, plain rubber butt pad, lever actuated forearm (splinter), basic engraving (in other words... not much), plain walnut (if this is plain I want some more).

They could not tell me if the 500 Nitro Express brass was the same as the 500 BPE brass that was original for my gun.

If it is I have a source for brass and bullets. I'll just load it with black powder and be done.

Please help, I really want this old girl to have a chance to hunt again.