BPE HEI Distributor

This engine is going to want AT LEAST 30* at idle & probably more like 35*.
The best, simplest way is to use MVA [ man vac adv ]. There is NO WAY that this can be done with a non-adj stock VA unit. I expect this engine would have about 10-13" of vac at idle & this will work perfectly with an adj VA unit. They have about 30* range. Turn the Allen Key fully CW. Limit the amount of VA via plunger travel. If your dist is a GM based, then Crane make an adjustable plate that limits plunger travel. Or, just make a plate that goes under the mounting screw. Measure the total plunger travel, which is usually about 9mm. This represents about 30*. So you make the stop on a proportional basis to provide 20* [ for the example below ] to allow 6mm of travel.
Example: use 16* initial + 20* MVA for 36* at idle.
The centri curve is THE LAST thing you do & unless you have access to a dyno, it just becomes an educated guess with modified engines.

D. Vizard has written over 30 books. The statement below is about ign IDLE timing, but it is in a Holley carb book. Hmmm? Ign timing in a carb book? And ign IDLE timing is mentioned more than once in this carb book. Hmmmmmmmmmmm? And it is because idle timing is sooooo important for idle quality, vacuum, cooling & tip in response. It is the FIRST thing you do when dialling in a modified engine.
Page 30: ' The optimum idle advance is typically about 35-40* for a short cammed street engine & [ though not commonly realized [ as much as 50* for a street/strip engine'.
I would love a dollar for every engine I have added MVA over the last 30 yrs that fixed low vac, poor idle, off idle flat spot.