Doug, you're at about the same place as Rommel was a short time ago. Check the "Timing Questions" thread. You should find some useful info.
Very useful info in Rommel's thread there is no doubt. I do need to point out that there is a difference between Doug's and Rommel's though. Doug has a 10-1 and Rommel's is 9.5-1. This 'can be' a significant factor. Come on Doug, pony up the extra $46 sents a gallon and see if the spark knock goes away. If you use octane to end the spark knock then you may find that you have more power because of it. I say this because it's the way my engine is. And I have to address the good point made that all engines do not perform better just because you add octane. BUT, some do.
It already went away with the disconnected advance. Therefore if the advance is still disconnected and he notes an improvement that would indicate he is still getting detonation that he is not detecting (I am assuming he is going by ear). This is entirely possible because under WOT you probably won't hear it. In this case you may be stuck with paying extra for fuel. Before you give in totally, I would try a colder range spark plug first (drop down in 1 range increments under you get fouling under part load conditions).
But if he does not have a problem with knock without vacuum then while it may "cure" the symptom to use a fuel with a slower burn rate, it's not addressing the root cause. Instead of spending 46 cents a gallon, spend $15 one time for an adjustable vacuum can and fix the problem.
You cannot increase mechanical timing and not compensate on the vacuum side for driveability.
