Couldn't quite get my head around why Steve opted to use a WRF axle over a YZF. He had told me it was too short, but end to end measurements were perfect. Given his current situation I don't expect him to sit around explaining things, and for good reason too! Thoughts with you Steve!
So with some measuring, we'll start with the brake side. The spacer is required to do 2 things. Set the center line of the hub, and align the rotor in the carrier. It does this. Then the hub is a constant, and so is the shoulder on both axles (YZF/WRF). The difference in shaft length is 20mm. Basically, when all is done with the shorter axle the shoulder on the floating side would be right on the seal lip, which leaves very little spacer, and a poor sealing surface. You could get around it a few different ways, but none are easy persay.
I'm guessing best bet would possibly be running with an axle shaft length between the two/a little less shoulder. I may get a mate to measure up a Honda CRF axle for exercises sake.