440 Engine Guru's Help

I see several possibilities here.
Firstly at idle
1) that cam has in the neighborhood of 100 degrees of overlap. Perhaps more. So for sure it will idle"rough"
2) the bouncing vacuum gauge needle, if a steady bounce may be normal, but if it's intermittent, it's a problem, and may be pointing you to the direction of the miss.There can be only one reason for that; a pressure spike is moving into the manifold from a cylinder.That means an intake valve problem.
3)The lack of vacuum advance at part throttle puts a severe handicap on the engines willingness to take throttle.
Without a well tuned PT timing system there are basically two times that an engine can have the right timing; 1) full load/WOT/ sometime around the torque peak, and 2) Possibly at idle.Of course this has almost nothing to do with your problem;jus saying.
Then at speed
You didn't say when the miss is occurring, but your first paragraph infers that you were driving it and possibly hard. So if that is right, missing under load is often bad plugs. Bad could be because they are carbon fouled, or overheated or cracked insulators. The CDI can easily light just about anything at idle to when it switches, somewhere around 3000 rpm. But after the switch it does just about what the standard system does, allbeit slightly hotter So a bad plug is still a bad plug.

So heres my 2cents; 8 new wide-gap plugs, and back up the timing to 30/32 and go for a new roadtest. If it's cured, maybe you can sneak in a lil more timing, but maybe bring it in a lil later.And figure out what killed the plug(s), and cure that,before it happens again.Ima thinking the fastest thing to kill a plug is wrong time spark, and second fastest is wrong fueling.

I once watched a guy build a Polaris triple(three cylinder) snowmobile engine.After melting it down in less than a mile, I watched him build it again. And melt it down again. In less than a mile.In frustration he finally asked for my opinion. I showed him the slugs and the plugs, and asked him if he knew why they looked like that. He did not. I pointed him to the Mikuni carb tuning guide. After a third rebuild,and a fresh load of fuel, he jetted up the carb for the current temperature and altitude, and had no more problems.
Two-strokers operating at temps that can vary from freezing to 30 or 40 below, are sensitive that way................................
More useless info, I know.