At a loss... HELP

Well this is a 264/264/110 cam with lifts of .440/.440
and the .050 is 220*/220*
with lash of .010/.012
So since you are having trouble with the vacuum, back the lash off to .013/.022 cold and start over. I'm betting currently, it is just too tight.Not that the spec is too tight, just that the hot setting may have ended up too tight. If, at.013/.023, it runs better,then it may have been that one or more valves was too tight, and now you get to figure out why.
A compression test before and after the re-lashing might be useful, or a leakdown test cold vs hot.
I also agree with moper in post#4, that you could easily crank in more timing; both idle and power.

My take on this is that your engine does not make enough torque at 700 to idle at the normal throttle setting. The usual culprit is idle-timing. But I have found slantys to be somewhat fussy about tight valve lash.
So in your case, if the assembly has been proved to not have any vacuum leaks between the top of the carb and the combustion chamber,and that the Vcan is hooked up to the sparkport, then increasing the valve lash will get you results. If it doesn't, then I would look at the cam timing next.
I hate to see you spend 3 days on the carb, when all the while the intakes were not getting enough seat-time.

I also think you have multiple problems.
insufficient valve lash
insufficient timing
lean carb circuits, other than perhaps the MJ
a lazy accelerator pump.

You can skip the valve lash and spend 3 days on the rest of the tune if you are so inclined, but I sure wouldn't. Then after re-lashing, you might be able to, or have to, undue the 3 days work that you previously did. So I highly recommend the lash adjustment first.

At this stage I wouldn't even put a timing light on it. Instead I would push and pull the D this way and that way, and let the engine tell me what she wants for idle-timing. I made the mistake of trying to force my ideas about valve lash and timing, onto my slanty once, and wasted many hours, not listening to her.Eventually I listened and that's when she woke up.