although I agree with the sentiment, said the engine needs more compression. 'That cam needs a ton of compression'.
We don't know CR from OP his engine, but like my engine has a 10.5:1 CR and still makes only 6-7" vacuum, little different cam then OP but duration at .008 is 283/291.
And that low vacuum is no problem, it is the nature of the beast, in this case a healthy engine will show a steady low vacuum signal.
What vacuum should OP have according you? What would you class normal for that cam?
I had spend my time setting up a Vcan, but since it only ends up in engine ping mine is disconnected and the engine is happy.
I tried with the stock Vcan that came with the MSD dizzy and also tried the Accel Vcan you mentioned, all sorts of combinations but wasn't going to happen.
It will only accept a rich idle mixture as you may expect with a cam like that, and a rich mixture burns fast so it cannot run with a lot of advance.
Without the Vcan it idles ok, instant throttle response and burns the tires clean off the rim if i wanted to, maybe it consumes a little more fuel but hey its a 440 and that will never change.
Showing all this information of GM is nice, and it would work similar on a Mopar,
STOCK version. The book goes by a stock engine with high vacuum, cams with low duration/low valve overlap and that is not what this is. Now you are facing low dynamic compression and more valve overlap.
It is not a race cam, but it already needs its own setup to run.
The debate of wanting to run low/high vacuum idle advance is up to everyone their own decision, if i could use the Vcan i would have for the purpose of getting a lot of advance at cruising speeds.
The fact is that OP needs to sort his fuel and air out before anything else as he has proven already his carb is not set right. He opened it so far as the engine wants air, even with a lot of advance it still wants that air.
He has to give that air first and the fuel to get a fuel mixture that is on the rich side of the line.
To aid in fine tuning it is handy to increase the initial to something high temporary to allow the engine to idle without having to hold the throttle open, but his engine will be able to idle fine at 850-900 rpm with 18-20* advance.
OP already hasn't shown himself for days anyway, i have given my opinion on what he can do to find a solution for his problem that i have come across before.