As long as you are 5+ over stock the bottle will fit. I mounted the bottle on the arm on my last bike. I had bolt on extentions. I chose to use the bolt on bottle clamp so I could return my bike to stock wheel base. But welding on will work to so long as you are happy with the extended wheel base.
I just drilled 2 holes, installed 3/8" nutserts and bolted the bracked on the swingarm with a small "L" shapped piece of aluminum to catch the bottle if the clamp became loose. I rode it on the street this way for a whole summer and never had any problems.