Make sure it is from 1957- should have wire key guards and not the kind held on by screws. Shooting Stars engraving with Conn USA on bell and 16M by thumbrest. Conn recycled serial numbers so 996xxx could be a 1978 MexiConn horn. If 1957 vintage other posts say around 200-300 in very good shape used, but in need of work to 500-600USD if in very good shape and playable as is. If a 1978 most would pass , 1970's Conns do not have a good reputation.