To me, your endeavor is quite awesome! I would give up my child (ok, not really) to have a piece of history, especially were it a family heirloom like that, which seems so much cooler getting it working AND working up a load.
It’s been quite some time since you initially posted this and I didn’t go back and reread it. Did it come with any sort of load information? Did you get a starting point? And did it come with a powder measure?
I have read how old guns like this often had powder measures made from antler or some such. But I’ve wondered wether or not they actually worked on load development or if they just settled on what they felt was a reasonable powder charge for their day. Powder, I assume, wasn’t a cheap thing back then and so I can see a very limited amount of testing. And the level of accuracy is dependent on the person and the use. 6” at 100 yds is good enough for hunting but not Xs. Not so hard to find and accept acceptable.
Please do continue to update!