I first saw those 600 components in '78 or so. 73 is the angle of the lug.
I'm guessing late '80s from the components and the frame geometry.
Looks like a nice bike, too bad they stored it outside for so long

Don't know what to advise, I know nothing of the brand. My thought is to grease the bearings, spray the inside of the frame tubes with framesaver, and ride the heck out of it. Don't know if you have to relace the wheels if the wheels can be trued, clean them off and try it out.