Using vacuum gauge to tune engine?

I had 14" vacuum on a '68 spec 340 with that cam and a Strip Dominator with a 625 Demon. I got my idle down to 800/750 in gear with a MP 175K convertor. It idled better with a Holley spread bore though. Hated that Demon, it was posessed with an ill machined needle/seat boss that would shear the O-ring every time you installed one and would always end up fouling the needle seat and flooding it. I would think a 383 would be more mild than a 340 with the same cam profile as that cam (031?) was called the "Road Runner cam" thinking it was probably mild enough for a stock 383 RR?