Getting the sprockets tomorrow, now I have to get this old one off, it's really stuck on, may throw a little heat on there. If I did everything right (I took the difference in thickness between a 530 and 520 sprocket into account) I should have near perfect alignment. I still need to make a roller for the chain to clear the swingarm pivot, but that should be easy.
I'm very eager to start the downtubes, the design I'm going to go with is basically the same as the sohc 750. I will continue the downtubes up to the neck, then make a crossbar to T across between them, and will weld it into the little stub of single downtube remaining. Should be plenty strong.