Nice work on the swingarm adapters Pete!
I'm a bit concerned with spacing the sprocket out that much. I know some guys who used to do this on their RFS supermoto bikes due to clearance issues with fat wide racing slicks, but they always had problems with sprocket bolts bending or loosening up on their 450s and 560. Now you've got 65 RWHP running through there....
Before welding the bushings into the frame I would do some testing to see how it holds up. One possible solution would be to simply move the swingarm over to the left a bit, and then lacing the rim with some offset to the right to center back in the line with the front wheel.
Proud member of the HUSABERG ADVENTURE TEAM!
12 690 Enduro-R, 12 Husaberg FE570, 09 KTM XC-F/ 450 RFS hybrid, 07 KTM 450 SMR, 09 BMW F650GS twin/F800GS hybrid, 03+05 YZF-R6