I don't have any specific suggestions for you, but I do applaud your decision to make something cool out of your existing Nighthawk, rather than building a chopper. If you've never ridden something with a hardtail and stretched forks, you're a fortunate rider indeed. No one should have to experience such dismal engineering and ergonomics just to look cool.
Building a cafe bike or streetfighter (or ???) out of an old UJM will give you something that looks cool and is actually functional as a motorcycle.
If you want to check out some ideas for a UJM build, check out this page. It features old Kaw KZ bikes, but the idea is the same.
http://www.stud.fh-dortmund.de/~stefan. ... reffen.htm