Join Date: Sep 2001
Location: Aurora, CO USA 80013
Likely it would take too much time, money, and effort than what it's worth to modify that Katana. There is not a big aftermarket for Katana's in the first place, plus your bike comes with bias-ply tires. That being the case, you'll be very limited in tire selection anyway.
In my opinion, if you're dead-set on having a wider rear tire, you'd be better off selling it and buying a bike that came with more modern/wider wheels and radial tires.
Why not just enjoy the bike for what it is, how it is, and just get out there and ride the wheels off of it until you can afford something newer?
"Fat, drunk, and stupid is no way to go through life son." - Vernon Wormer.- Dean, Faber College.