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I think 18-20 initial is a good move. Get rid of the vacuum advance and use just mechanical adv. If you start with 20 initial, then you only need about 14 mechanical to peak at 34 total. Your mech adv mechanism will need to be adjusted or modified to limit the range of advance to 14 degrees. The MSD billet distributors use bushings, the duraspark style require that you bend the little "ears" that stop the advance mechanism from turning.
20 initial provides more time for the fuel to burn at low engine speeds. You will notice that the rpms increase by simply advancing the idle timing. This allows you to close the carb butterflies to lower your idle speed. By closing the butterflies more, you increase idle vacuum and low-speed velocity through the carb. This allows for better mixing, better low speed combustion and better throttle response. This is how most modern carbs are designed to work. You cannot dial-in your carb until you address the initial timing issue. 20 intial helps the engine run at idle..otherwise, you play games with the carb's idle circuits to try to help the engine run at idle....since the carb's idle circuits have a big impact on the mid and high-speed circuits, the engine will run poorly throughout it's range if you don't get the idle squared away first. Lots of initial timing is used to simply help the motor run at low speeds with agressive cams by providing more "burn time".
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