I own a pair of JBL L150A and if I'm not wrong they were manufactured in 1982...they sound great !!!
I changed the foam a year ago and they are in like new condition, replacement parts for older (good ones) JBL speakers are quite easy to get.
And for the exact definition of what a studio monitor is, I really don't know so I'd preferer not to speak.
Go for them.
Rgds,