carb tuning help

I've got the same ingnition setup and have spoken with Don at FBO, in fact he talked me out of the 10* bushings because I have a vacuum advance on my pro billit dizzy. He advised me to run that off of manifold vacuum so that it would pull the initial timing way up but drop off by the time the mechanical was kicked in. I have to admit though, I don't have it completly dialed in yet. It wont even run with the vacuum advanced not hooked up because it drops the initial down so much so I had to start it up and plug the vacuum adnvance off while feathing the throttle to keep it going, then you can confirm the total timing.
However, I too am very new this. Cracked - how do you discover what the engine wants for initial? Is it the advance till the starting gets rough, then back off method you described?