I've had trouble with this stuff too, even if the spinner and prop are balanced. It's probably a good idea to set up a dial indicator to make sure the adapter is true. If that's off, it makes it just about impossible. After static balancing, I usually run things at low power and feel for vibration. Then I stick a small bit of tape on a blade and see if it gets better or worse. Worse and you swap to the other side and try again.
Tru Turn has always been pretty good with balanced spinners, but it wouldn't hurt to check it too. If you have a long 1/8 shaft handy, you can put the adapter, prop and spinner all on that and stick it on your 4 wheel balancer.
I hate to say I think 1/8 is too small, but don't let me stop you from at least trying it.