Ed Parry has one for sale as we speak.
It was made up from The Rifle Shoppe castings. I've been to Ed's place. It's nicely made. I don't believe the stock is bored for the yoke. He says it's deadly accurate at 5 or 600'. As Mike says, that's a 1" ball, about 35 lbs. No wonder the British used them in the field, from carriages to lay cover for the cannons or from ramparts or ships rails.
Ryan