Timing by Vacuum Reading?

I have a rather modified engine, high compression, large cam, 408, and I need to know what the best way to time it is because there is no standard measurement for it. I can start with the recommended timing, which is 10-16 Initial, idle in other words, and ramp it up to 34-46 at approx 3000 rpm, but there is a huge difference between 10-16 advanced.

My buddy said that I can use a vac gauge, and set the timing to make the vacuum gauge read its highest vacuum reading. Is the a good way, some sort of starting point, or what?

I have always had pretty stock engines before this 408, I have an MSD 6AL box, w/a MSD Mechanical Advance Dizzy, no vacuum advance on it. I will probably get a million different replies because this is not an exact science, but I need to know.

Thanks