I taped the vacuum gauge to the windshield and went for a drive in a number of conditions (fast, slow, slowing down from fast, up a hill, down a hill, cruising at 60mph on a highway, etc) and my trusty sidekick (da wife) noted that the highest the vacuum went was 18.
I looked into the vacuum can that came with my new MSD 8362 and they are no longer adjustable but MSD provides a stop plate that, depending on how you install it, will limit your vacuum advance.
There are 4 positons it can be installed in, A=14 to 17 degrees, B=11 to 14, C=8 to 11 and D=5 to 8. I'm going to install it as B as that will ensure it does not go over 15.
That should then complete my timing setup and now next steps are the Holley finetuning... Idle Mixture, secondary kickin, verify power valve, verify transfer slot is not too much, off-idle setup, etc. Lots of reading to do..