Disassembly of the Sharps is pretty easy; I don't have a good nomenclature guide, but here goes.
On the right front of the receiver, just behind the foreend, you will see a lever and a little round pin. Push in on the pin until the lever can be swung forward and down. After it clears the lip on the receiver, pull on it and the long pin should come out. Then the breechblock and breechblock lever should drop right out. To remove the sideplate, cock the hammer and remove the screws on the left side. The sideplate and hammer should also come out. Disassembly of the mechanism attached to the sideplate is normal, but be sure to use a spring vise or a tool like that issued with the Model 1873 Springfield to keep the mainspring under control so it can be replaced. If you remove the hammer, do it carefully, in the same way as for any other rifle of that type.
Center fire breech blocks have been made and were advertised in the Civil War magazines, but I have lost track of sources at this time. Maybe someone else can help. (Of course, Sharps made CF breechblocks for their own new rifles, but I don't think they interchange and would in any event be nearly impossible to find. Some brass case reloadable ammo was also available.
I am not sure how much work would be involved in fitting one of those breechblocks, though it was often done and AFAIK, the gun could be put back to original configuration.
Try
www.ssfirearms.com for the sight and other parts. If anyone has them, S & S would be the ones.
Jim
