vacuum advance or not?
 

Rob,

I agree that 5 degrees is a little light for static timing. If you need the additional advance to get the car to idle correctly, you'll have to adjust the mechanical/centrifugal advance limit to offset the difference.

As it stands now, your getting 27 degrees of centrifugal advance. I wouldn't suggest going more than 15 degrees static advance. Going too far can cause some starting problems, unless your ignition box has a retard feature during start up.

Vacuum advance is usually connected to a port above the throttle plates and provides some lead time with slight throttle opening when slowly starting off and at part throttle conditions while crusing down the road. Under full throttle conditions where low or no vacuum is present, vacuum advance is not in the picture. Also, with total mechanical advance comming in at probably under 3000 RPM with your motor, I wouldn't think you would benefit from any vacuum advance.

Now, if you were to connect the vacuum advance to manifold vacuum, you would see vacuum advance at idle. And you could adjust it for say an additional 10 degrees of advance. The one problem I see would be when you step on the gas..... vacuum goes away and the additional advance goes with it.... possible off throttle stumble.

I'm not clear if your dizzy has or doesn't have a vacuum advance on it. If it does, try hooking it up to manifold vacuum and see how it performs. Trying it is a lot easier than pulling the dizzy and adjusting the mechanical limits. Who knows???? it might work...

No vac advance.

Try starting with 14-15 initial, and another 20 centrifugal, bringing total to 34 degrees.

I have a 393 with Duraspark, Speed Demon 750DP, Mallory HyfireVI and vac advance. Here's the way mine runs best:
20 degrees at idle, 36 at 3000RPM, 46 with the vac advance hooked up at 3K. The Crane recurve kit works well.
I ran without vac advance for a while, but the mileage was killin' me. The vac advance adds about 25% to my mileage.
Too much vac advance causes a high-RPM/light-throttle misfire.

HTH, Ed