George:
Its difficult to determine what cannon is in your pictures. I believe this gun was shown on this web site before because it looks familiar to me. I believe the best quess at that time was that the gun is a reproduction of more recent times. If it is a reproduction, its value would be much lower. The rough appearance of the gun, carriage, ammunition boxes and the breech assembly again suggests a more recent home made reproduction. These thoughts are only suggestions and you need to have a expert appraise the gun.
A note about the manufacturing of the gun. Street, Hungerford & Co. of Memphin TN did make 10 of these guns but none of these are known to have survived. This company made cannon for the confederacy for a short with production ending in May 1862 when the federals captured the city. Their firm was known for poor quality production. Tredegar Foundry in Richmond VA made a 1.57" iron Williams gun and four of these still exist today, one of these is at the New Market VA battlefield park. Can't find much info about Tredegar models of Williams Gun
Ron