Yes, another timing question!

5" of vacuum is really low and in the most aggressive of cams territory. That you got the vacuum to double by advancing it says it didn't have enough initial. The idle smell will be better and smell cleaner since the engine will be running more efficiently.

Like the other guys mentioned. Verify tdc on your balancer. Make sure there isn't any fuel dripping in the carb at idle. If it will start in the 20-22 initial range when warmed up, run it there would be my choice to start. Low compression and big cams can take a lot of initial and still start/run OK.

The carb idle settings will change when you advance timing so vacuum could increase even more.

Please don't drive it around with the current distributor mechanical advance and 20+* of initial. You could try bumping it into the 40+ total range and listen for detonation, just be careful! I get the feeling you know that already.