"A 260" fits the rear fender on the right wheel width but it's good to check the specific tire manufacturer's website for exact actual width because Avon tires tend to be a hint wider than other brands in the same width category. That's why I think sometimes someone does "a 260" and the stock fender strut bolts interfere. While on the manufacturer's website you can also check the rim width recommendations for each individual tire in order to maintain good tread shape on the road.
In this case the Avon Cobra Chrome 260 is 260mm and likes the 9-inch rim, and the 250 is 251mm wide and also likes the 9-inch rim.
I seem to recall the old Metzler ME880xl in 260 would most often fit the Warrior rear fender but need to verify, will try to get time soon. Or maybe Kyle or other members with the mod will chime-in. I'm no longer finding the tire specs on-line for that tire so will find our old tire specs thread to get it.
The modern Metzler is model 888 in 260/40 VR 18 M/C (84V) TL but again no width spec found on their website.
Here is the old and outdated thread covering rear tires:
There is also a front tire thread with similar title.
The reason for posting it is because the old Metz880 in 260 was often used by all the swingarm builders back in that time (2011) to fit under the stock rear render, so it might help make this decision.
But I would also really like to hear KyleNV's knowledge on this because he has so much experience.