Trying to diagnose timing, vacuum and stutter.

1965 SBF 289
bored.060
edelbrock intake and carb
comp N+271H cam
shorty headers

New plugs, wires, coil, distributor (condenser and points).

I've got a stutter (rough running engine) when I hold a consistent speed/RPM. I don't notice it when creeping below 1000RPM. The car starts easily and idles fine, under acceleration its fine too. Just when its holding steady, or trying to. I'm thinking it might be related to vacuum advance but I'm not experienced with that and really don't know. Its just a hunch. I'm hoping its not a blown head gasket. I set timing to 12* BTDC using a timing light and checked vacuum, the vacuum was around 12. I tried following a "how to time SBF using a tach and vacuum gauge" and the way it read would really advance the timing which I found odd. Vacuum increased to roughly 18 but I had no way of knowing what my timing was via light because my marks only go up to 12, but if I had to guess it would have been near 18* BTDC. I set it between 12 and where I found best vacuum and that made my starting a lot easier and produced more power with no knock but the studder got worse. That's what has me leaning to vacuum advance issues but again, I'm not experienced with that and trying to work the bugs out of this is driving my bananas.