What is the "right" amount of vacuum for a stock motor?

[davepl]

My 402, which we rebuilt entirely stock except for the cam (bear with me), maxes out at just under 15" of vacuum at idle in neutral around 650 rpm. That's more than enough for brakes and so on, but I want to know if I've got it close to stock.

The cam is supposed to be as close as we could get to the 310hp cam. It's 214/218 (110 degree intake center, 66 degrees overlap).

I want it to run "like new", not a little better than new. It did pull 323 on the engine dyno vs a rated 310 so it's darn close. That was probably with headers, but that's probably how they rated them gross in 1970 anyway.