Nice hot rod, welcome aboard!
Would you feel comfortable trusting your spouse or child on one?
In the Documentation forum is a section with pics and parts views for things that differ between model year. One of the attachments is the seats for 2002-2003 and the seats for 2004-2010. There is a bolt-on loop toward the rear of the fender to hold the back of the passenger seat. And there is a bracket to hold the front of the passenger seat. Have a look.
Then, you can go to any Yamaha or dealer website and bring-up oem parts. Browse to your model year. Then find the seats, then view the drawing for the bracket and/or loop you need (get the fasteners too). Then scroll down for the part numbers list.
Its worth it just for peace of mind!
Also, the 2004-2010 passenger seats come up for sale here all the time. Most times the prices are real good.