Welcome.Mid/ late 60s is probably as close as you can get. (The one that I had,very near the end of regular production,was #144,xxx and made in 1972)
If you read the threads here about Trombone dates,it's just interpolation from a handful of known examples. There is no resource for manufacturing dates.
Last edited by Camster; 04-20-2017 at 09:52 AM.