OK, stupid question #1 (it's early in the day, so I'm sure I will have more).....did you turn yours all the way with a small allen wrench?
Honestly, I have no idea what they "should" advance since mine has been disconnected for years....but
1. Maybe you could modify the little arm that attaches to the advance plate in the distributor to get more advance? Or the advance plate itself?
2. Maybe you figure out a way to use one of those circular "vacuum booster" things I've seen on early 70's small blocks to boost the vacuum signal?
3. I'm just shooting from the hip here.....not really sure about any of this.
Lastly, why do you need more vacuum advance? I've got so much initial timing on my motor I'd knock on race gas if I hooked up the vacuum advance.
Oh yeah, all the vacuum advance pods I've ever seen were adjustable.