First advice, most of the regulars on this site have interest in performance motorcycles, race modifications and restored classic motorcycles.
Firestone tires lol (aka Clown Shoes) most here will point and laugh.
Your problem doesn't stop at the swingarm, the rear sprocket has to line up with the countershaft, how much clearance do you have now between the chain and rear tire?
#3 extend the swingarm sounds like your easiest modification
or even better; buy a wider 17" diameter rim plus new spokes to suit, then re-lace the existing hub, that will give you a far better selection of performance tires and give you a little more clearance at the front of the swingarm.
Firestone tires lol (aka Clown Shoes) most here will point and laugh.
Your problem doesn't stop at the swingarm, the rear sprocket has to line up with the countershaft, how much clearance do you have now between the chain and rear tire?
#3 extend the swingarm sounds like your easiest modification
or even better; buy a wider 17" diameter rim plus new spokes to suit, then re-lace the existing hub, that will give you a far better selection of performance tires and give you a little more clearance at the front of the swingarm.