Using vacuum gauge to tune engine?

“I moved this update to a this new thread because I wasn’t getting feedback on what to do next in this situation.”

I recently took my edelbrock performer rpm intake to a machinist I trust explained the situation to him and had him mill my intake .040 on each side. That is the same thickness as the two felpro gaskets under and above the valley pan. The intake lined up perfectly now with the gaskets and I’m glad to report no intake or carb leaks. Checked for leaks with starter fluid previously based on the engine idling much higher than before it was taken apart. It used to idle at @1000rpm and with the leaks I had it idled noticeably higher at 1500. Now it is back idling at 1000 again. I sprayed the starter fluid at various points where intake meets heads and carburetor gasket with no sucking in of fluid or change in rpm as it did before. I hooked up a vacuum gauge to the constant vacuum draw on the side of my speed demon. I hope this is the correct port to use for vacuum testing? At idle it currently has 10-12 in vacuum that is after I moved the distributor around to find the steadiest and highest vacuum reading at idle.

However, it seems like I have another issue. The engine doesn’t idle as smooth as it used to and the gauge bounces around by about 2 inHg. I should mention that it is a 383 4 speed 67 Dart with the older Mopar performance camshaft 484 lift 284 duration. What would be my next logical step check plugs, wires and distributor cap or is idle mixture screw on speed demon carb off? Should I pull each plug wire off of distributor cap one by one and listen to see if I can find if one is misfiring or dead? Some are a bear to get to with TTI headers. I didn't touch the carb just put it back on after changing old cast iron to edelbrock performer heads and updating Harland sharps with Mikes geometry kit from B3 racing. I’m trying to get it running as smooth as it did before by process of elimination and learning as I go. I have included a video of the engine idling and the gauge. When I rev it up it also feels like it is running rough.