Manifold Vacuum Advance what am I not getting?

Mbaird,
I can guarantee that your engine will idle better & have more vacuum with more timing with that cam & 360 cubes. My guess is 35-45* at idle will be optimum. You are going to this by electronic means? It needs to reduce timing as the engine comes under load or you could get detonation. That is why the simplicity of a vac adv unit is so good: it does this automatically.