I like Dan Jensen and follow him on tips and tricks when it comes to tuning Pontiacs. I've had pretty good luck doing this:
Total mechanical advance from 36 to 42 degrees, and I try to get it in by 2,500 rpm. That’s a lot quicker than the factory setup that brings in all the advance by 4,000-4,500 rpm. With that said, every engine is different and some experimentation is required to find the sweet spot.

“For a high-compression engine with a mild cam, I’d probably want a little more mechanical advance because they can’t tolerate as much initial timing as a low-compression engine can. Most 400s [except Ram Air IVs] have 10 degrees of initial timing, but I like around 12 degrees initial timing as a rule of thumb. Pontiac engines seem to like that.”

With initial timing set to 12 degrees, and mechanical advance bringing the total to between 36 to 42 degrees by 2,500 rpm, some additional tweaking will get you to your engine’s optimum setting.