There isn't much to them really and I don't think instructions would help much but maybe someone has a copy that they can photo and post here.
In the meantime, here's what mine looks like. Note, the grip screw and the rear sideplate screw are the same. The short screw goes in the front hole of the sideplate.
Do NOT lose the nipple. It is a odd size and it is difficult to find a replacement.
Also, if you plan to shoot it, it would be worth your time and money to go to the local hardware store and buy an "Aircraft length" 3/32 or 1/8 inch drill bit.
At the bottom of the bore you can see a very small hole in the face of the breech. This hole connects the breech with the front sideplate screw hole which serves to transfer the blast of the percussion cap to the powder charge.
As I say, the hole is very small and it doesn't work well.
Use the Aircraft length drill (usually about 6-8 inches long) to drill out that small connecting hole. Be careful not to drill too deeply. You only want a clear hole to the depth of the crossdrilled screw hole. If you drill too deeply it can end up creating a hole clear thru the cast boss that the screw hole is in.
Doing this drilling will greatly improve the reliability of ignition.