Cool project! I am using Harley hubs front and rear on my CB750 tracker project. The great thing is that they are 52mm OD (at least in the rear haven't checked front I have the same front hub as you) and bearings are easily available that have a 25mm or 20mm axle size The weird thing is I am mounting the front hub up to an Aprilia Shiver 750 front end...what are the chances? You are correct about the front hub weighing a ton, I was shocked when I took it out of the box. Since you already have the front, it would be simple to get the rear Harley sportster hub. I do know those have a 52mm OD bore and a 6304 bearing gives you 20mm ID , 6205 is 25mm ID. And getting rims with 40 spokes is dead simple and inexpensive. Can't wait to see what you come up with.