360 runs great one day and then poorly the next

From your descriptions, I don't think this is your problem,but To check if the running fuel level is stable,
With the engine idling clamp the fuel line.
One of three things is gonna happen;
A) If the fuel level is too high, the engine will slowly smooth out and pick up rpm, then continue as at B) below
B) If the fuel level is about correct, nothing will happen for about 15 to 30 seconds, then it will slow down and continue as at C) below.
C) If the fuel level is too low, the engine will slow down, run rough, and eventually stall.

I also am wondering if you have an intermittent vacuum leak, and because of the severity, Ima thinking the PCV is cracked. I've even seen them broken and the only thing keeping it together was the engine vacuum.

If you thing it's ignition;Isolate the cylinder or cylinders. Just pull one wire off atta time (engine running of course), looking for wires that make no difference. Then you just have to prove the wire, the plug, the tower, or the valves are closing..