No problem going against the grain- I do it all the time
Happy to debate the approach.
Issue with setting it to "stock" is determining what that is with an unknown distributor and cam, pistons, other critical parts likely changed.
I just looked at my Chilton's (first time in many years) and the base setting for a 67 400 is 6 deg. So assuming the engine is 1967 and knowing there is 18 deg advance in the distributor that would only give 24 deg total advance. I know from experience that is not right. My cars wouldn't get out of their own way with timing set back that far.
For 1969 the base setting is listed as 12 degrees. With 18 deg centrifugal in the distributor that would give a total of 30 degrees which is very close to where he is now. It is very possible that the distributor is original to the car even though the engine has been swapped so that would be the correct "stock" setting, all things being equal. For optimum power I think that it should be a bit higher than this, but at least it is in the right range and the engine should run good.
Agree we don't know what vacuum can is on the distributor. Also don't know the mechanical curve. But since he is looking for the power then the total advance needs to be reasonable. If it causes pinging under light load with the can that is on it then that will need to be addressed. But I would not disconnect the vacuum advance unless it is causing problems.
Darth, understand that your priority has to be getting past inspection. But when you get back to engine tuning vacuum readings and some road testing would help.