You are not going to find a real answer. It is all an educated guess. The valve timing events, ignition flame front, sharp spots in the combustion chamber, and other things that can't be calculated easily will limit the accuracy of your guess. You can estimate and try to get in the ballpark. If you get detonation at low speeds you will need to drop your timing a couple degress, or change cams.
With only 216o duration at .050", I would aim for 10:1. With this ratio, cam, and octane, you should be pretty safe with up to 34o total timing.