A "The Martin Magna Tenor" in good playing condition is a very good horn. They reached the market in the mid 50's. A plated Magna with silver neck pipe is a sax that would give you the money back the day you want to sell it! Even the ordinary "The Martin Tenor" is a good sax. Some players perfer the older ones to the younger ones. I have tried Martins from the 40's but I couldn't hear any difference. I had the same feeling that I have on my Martins from the 50's. Make sure that "The Martin" is correct setup. IMO thin pads (0.160"/c 4,00 mm) or thinner. Low keyheights. Pads with resonators makes "The Martin" more contemporary sound wise.
You should keep in mind that "The Martin Tenor" is a construction from the mid 40's. The ergonomics are not as good as on modern saxes. Toneholes are in-line and bell keys on left side on the bell. If you live with that you'll find "The Martins Tenor" very good saxes. I don't play my Martins so much anymore. Not good for my hands, wrists and back. For me it was a matter of quit playing the saxophone or to find a modern sax with better ergonomics. I bought a Yam YTS 25. A good player for the money and easy to own as well.