so balancer arrived. Pioneer DA-3021. Not a bad piece.
For original plan was to take 0.100 off this face here. I'd cut the spacer on 0.100 thick material and just sandwich it
Of course, I got the Hub ID dimension wrong. Good thing this was a cheap Alum prototype. However my multiple bolt idea looks pretty good. I can just pull crank pulley and adjust if needed.
However, this looks awkward
So gonna think about this and a few ideas that have been mentioned. Might try something that attaches to pulley, or go behind balancer. My goal is easy bolt on with no special tools (well other than a 2500 watt co2 laser cutter)