Details, Man...I wanna have details!!
I'm really happy for you and compared to prices I have seen here in VA in the USA, it would appear that you got a very good deal. The main detail I would love to have is the name of the manufacturer. Ballard himself didn't ever manufacture the rifles, so there will be a name like Merrimack Arms, Dwight, Chapin and Co., etc.
As for shooting this old piece, the original ammo was rimfire, I believe, which is long out of production, but there have been some rather clever conversions done as well as some ammo made using cases that accept a blank .22 rf that acts like a primer for the assembled round. At one time, Dixie Gun Works in Tennessee was making some of that type of brass. On the other hand, if I were around a talented machinist as you seem to be, I would look into having a replacement breech block made with a centerfire pin, then make some brass to fit the chamber and shoot the rifle otherwise unaltered...I would hate to make an irreversible alteration to something that had made it 140+ years unchanged.
Again, congratulations on an interesting find and keep us posted with your progress.
Regards,
Froggie