A long time ago, I decided to go the 300 tire route. Before I took off the stock wheel, I marked the tire lip area on the swingarm. I made the cutout on both sides and took it to a local fab shop and had them weld in sone .061 aluminum filler plates. $35.00 If you do this, get a stout allthread with 4 big washers and 4 nuts to lock the area where the axle goes thru both sides. The arm likes to twist when it is welded on. I got some pics from Dam Guy and Rainey about the fender details (probably some others also). I used an air grinder to split the fender stiffeners on both sides, beat them flat and welded them up with a mig. I cut off the straps that are tack welded on, grind off the screw inserts, flattened the indentions toward the front---didn't think about cutting them out---good idea. Took a screw jack and spread the fender supports.
I have the Avon and I still needed to sand the drivers side tire edge. Just need an eighth inch shim, but didn't have time to make one. I have 2.75 bones and if I have a rider or hit big bumps, something rubs, just don't know what. I have some 2" bones I think I will swap out this winter.
It's really not a hard mod if you have some tools--and a little time. I have the stock exhaust, so it has to come off to change the tire. Extra 10 minutes. I like the 300 look, its really like anything else, new handlebars, new seat, paint. If you just want to do it, DO IT.
dw