value of JBL L-65?

I don't know about L65s but I have a pair of L100s and a pair of L40s that I also bought new in 1976 and 1977 respectively, and I do occasionally surf the market to see their worth. I have seen L100s in perfect shape bring as much as $700-$800 and the L40s about ~$300, maybe a little more, depending on the condition. I didn't keep any of my boxes so you'll probably get extra for the boxes, etc. It all depends on the condition of the drivers, cabinets, and the grills.

You're welcome. With the exception of a few special models, and either as a rule of thumb or just by coincidence, you can figure on recouping the original retail price or may be slightly more depending on location, when selling most vintage JBL speakers. Of course assuming excellent cosmetic and functional condition.