I tried calling Don today and he was on the other line with an overseas vendor and did not have time to talk. But I emailed him my question on what is the lowest engine vacuum that his distributor is setup for, and he was supposed to respond to me tonight. I am hoping that he will give me a straight up answer (10"hg, 12"hg, etc.)
Once I know this answer then I can start tuning my in D mixture.

Thank you for adding his tuning response to this thread.