You should have that B72 any day now. That's the seat I was going to use on my skinny tire cruiser.
As for the springer, just an idea, if you could put a forward angled curve in the struts that go from the springs to the axle, you would lower the front slightly and move the front wheel away from the down tube of the frame.
But on those springers, I've always had old ones with weak springs that would bottom out on the tire and flip me over the bars, so maybe some kind of stops would have to be made.