Does anyone have the actual width, in mm, of the K100 swingarm, bearing face to bearing face?

310mm by eye with a tape measure. If you need it more accurately let me know.

FYI the swingarms on the oilhead boxers (R1100/1150) are the same, just a lot longer because the engines are much shorter.

MILLIMETERS??

Do you want me to send a ruler across?

My ultimate goal is to use the K100 swingarm in a single sided leading link front end for my R90/6 rig. I will use a hub bearing assembly bolted to a bracket to bolt to the drive end of the swingarm, with spacers to adjust the trail. I also have a K100 swingarm being modified to fit the R90 frame. The driveshaft was modified to mate to the airhead transmission output flange. I had this done years ago (by Bruno's in Canada), before you could buy an adapter spline. With the stock 2.91 final drive and a 175/55 R15 auto tire, I come close to an effective final drive ratio of 3.33, which is reasonably close the the 3.36 I currently have.

Chris, I have seen several examples of airheads using the R1100 - 1150 swingarms and the now available adapter spline. The airhead swingarm is considerable narrower than the K100 swingarm. I wonder how they make this work.