suggestions on timing on 70 340, programmable ignition

Alright... just to update I did install the msd system... and contrary to the manual and what it says in the tuning interface, it does read vacuum,,, but it displays the absolute pressure in positive psi which can be confusing... so what they sell as a 30psi sensor is reall -15 to +15 psi.


How much should I advance the timing at vacuum?