Funny thing about McDermotts, when I starting playing in the late 80s, they were looked upon as cues that hacks used because they did not know any better. All the "good" players used a Joss or a custom (Lambros was huge name in MA for one).
Now it seems they are more highly regarded. An early 80s McD is probably worth quite a bit more than when it was new if it's in good shape.
fyi, if you tried to sell, you will have a tough time getting 690. If I had to guess, in this economy, I would say it could fetch around $400 or so if you found the right buyer.