I am wondering about the vac advance question. Vac advance is very important to your engine. It is not a nice to have. Do your research. First step could be to read the instruction manual of your distributor...
Then you have to measure how much vac your engine produce at idle and with full open mech advance (~3000rpm). Sum of mech and vac advance must fit your engine specs. Otherwise you must adjust mech and/or vac advance. On newer distributors this will be realised with e.g. microswitches.
I fully agree with olddog
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