Yeah. That was one of the hardest parts. Figuring out how to line everything up in the back. Did you get the wheel from mcworx? If so, you should be able to use buell bearings and axle.
The Buell definitely has a bigger axle and bearings than HD. The original rear pulley was also a specially machined sportster pulley to fit that wheel. The axle will fit sloppy in any wheel. There is a spacer that slides over the axle - between the bearings.
Keep the offset sprocket. You need that. The frame was designed to use that sprocket for a 250 tire. It’s also an 883 sportster sprocket for a little more off the line. 
First, try the bearings and spacer from the Buell wheel. If they don’t fit, you’ll need to go with a 7/8 axle and might need to rework the axle sliders in the frame. Roll-on cycles in Oakdale can get any size sprocket spacer you need.