A few thoughts. First If I had broken pieces of anything under my rocker covers I wouldn't even start it until I was sure there is no debris anywhere in the oil system. Any little pieces of fragments of metal that get into the bearing areas and you can start saving for a complete tear down. Draining the oil through a paint filter and opening the filter to check for metal is the very least I would think needs to be done.
Replacing broken components the running the engine without first determining the cause of the original breakage is another thing I would avoid. Those components broke for a reason, replacing them without rectifying the initial cause is asking for more broken parts.
Idle smoothing out when pulling a plug wire may be due to a screwed up valve timing, firing the cylinder when the increased pressure slows the rotation rather than increases it.
If it was mine I'd pull the engine and do a complete teardown and inventory all the component specs just to see what's there to start with. At the very least I suggest pulling the heads and camshaft. Until you know what you have in there it'll be a bit difficult making an informed decision as to the best course of action to rectify your malfunctions. With the heads off you can measure the chambers, inspect the pushrods, guides, seats, cylinder walls, lifters etc, You can also measure the stroke to see if someone dropped a larger or smaller stroke crank into the block as well as determine the deck height, measure bore, measure the camshaft lobe lift, check if the camshaft has any lobes worn right down, etc.
Vacuum gauge needle will always drop during acceleration. At idle or cruise the throttle valve is almost closed or only slightly opened. The area above the throttle valve is at atmospheric pressure and the area below is at a reduced pressure due to the downward movement of the pistons on intake stroke. When the throttle is opened the pressure differential is reduced and the vacuum reading drops.
Back in the good old days when the lifters were solid, guys used to glue pads to the underside or the rocker covers to dampen the valve train noise cause by valve lash. I kinda like the sound of mine. Also It's easier to hear any changes in sound due to an increase or decrease in lash without the pads.
