I've caught quite a few ling on Nip in past years.
6lbs test is fine.
Find deep water (25-35fow) in shoal-y areas. A large minnow (4-6") on a hook or mid-sized spoons will work. It's difficult to 'target' them, but I've noticed that they will crowd an area if you provide a lot of bait. They'll stick around for a couple or more days.... I know this because I've found hooks and/or lures in their bellies from the preceeding day.
I haven't targetted them specifically, but if I were to, I would look for areas with a lot of perch, keep a few perch, fillet them and throw some carcass down the hole. Also, I would pop and drop all my remaining minnows down the hole.
We've caught many ling during the day, but generally it's better at late dusk. I don't fish at night typically, so I have no idea if it's any better at night.
Good luck!