can't you turn the back of the hub flat to suit and mount the disc you have from the back instead of the front? same result as buying deeper discs and you've got access to the lathe so worth trying before buying more parts.
neil.
1. That would lose the structural bracing that the HD rotors came with. I like those and wouldn't want to give them up.
2. Any brake job after the first would require removing the hub to get the rotor off. I had a Honda that needed that and instead of new rotors it got new pads and grooved rotors because I had neither the time, nor the money to do it right.
Unless it came down to a horrible alternative, then wouldn't put the rotor on the inside of the hub. Just me though.