check the General Marlin Identication subforum as they have a link to help date particular Marlins. the peep sight could have been factory installed or added afterwards, as they probably had several different sub models of the 39A. to determine it's value or worth, take it to a competent gun dealer and have him do an appraisal of it, based on Blue Book value.Just inherited a Model 39A with Serial Number of 6097. What year was this rifle made? It also has a Marble Peep Site behind the Hammer. Was this standard from Marlin, or was this added after market? How much is it worth? Good condition!