My directories only go back to
1967 but 12834 was assigned to Gates that year. There is no Gates entry in the alphabetical listing. In 1970, 12834 was assigned to Allan and Thelma Weygandt from Detroit, MI. In 1989, 12834 was assigned to Weaver. We can not tell when 12834 was put on that particular trailer, so we can not say who owned it at that time.
The value is what you can get someone to pay for it. If you hire the work out you will likely not get your money back in the selling price. This is before torque axles, so if the springs are good you may not have to replace axles. There are several people on this site that sell some reproduction parts.