A ton of reading up on Vac advance and why would be a good thing.
Manifold vac is in full advance at idle and ported is for zero advance at idle.
They are two completely different functions for different reasons.
Ported came about to make engines run hotter for emissions at lower/idle RPM's
Manifold gives full vac advance at idle and backs it down as engine load goes up via throttle plates opening and lessening the amount of available vacuum.

With a stock style distributor I think you'll find that setting it at 8-12 initial you will end up needing to limit the mechanical advance so you don't end up with way too much total between initial and mechanical (which is a normal thing to do)

I recently found a good writeup on it and I'll see if I can find it for you.

This one is a good one to start with.
http://www.hotrod.com/how-to/engine/mopp-0301-mopar-electronic-ignition-system/

 

While TB and I agree on ported vacuum, the problem is that there are "two schools of thought." Some advocate using FULL vacuum, and IF YOU DO THAT you will need a completely different mechanical curve.

With the way 'we' think, IE ported, timed, no idle vacuum.....

8-12 initial is nowhere near enough.......

you definately want vacuum disconnected at idle

if you go to the Edelbrock site, there are downloads of manuals for the carbs which tell you all you can imagine about them

There has been TONS written on this site about timing.

Here's one

http://www.forabodiesonly.com/mopar/showthread.php?t=158842

and

http://www.forabodiesonly.com/mopar/showthread.php?t=150251

One thing you need to keep in mind. All factory distributors 69 / later are "smog" advance curves, not what you want for performance, and they get worse up into the mid 70's. "Long slow" advance curves as opposed to "fast and short"

This means you either need to replace the smog factory distributor with an adjustable aftermarket one, or else recurve the one you have

 

Thank you.
That's the one I was looking for, but it's on my home computer and I'm not at home.