Well, if you want Duratec UDP's, good luck. SHOShop made some a while back, but they're very rare anymore. The only person I know that has them is Venom.
As for the Vulcans, well, there just aren't any. There are some for the Rangers, but I don't think they'll fit.
I installed a set of UDP on my 1991 SHO. The claim is for about 5-8hp all across the rpm range. The main benefit I wanted was longer life on the accessories and 8000+ rpm rev limit. I am sure if you pulled the pulleys off your alternator, water pump and power steering you can find some one to machine smaller pulleys for you.
Under Drive Pulley---makes the belt-driven accessories run slower, freeing up more power. In the high-revving Yamaha motors, it also helps prolong the life of the accessories, since they'll fail in the upper RPM's way before the engine does.