Dead hole. What’s the next step
If carb not at WOT;
Not good enough; air could be transferring to another cylinder, under a closed throttle valve, and exiting somewhere else.
Pulled dipstick. Nothing felt
Pulled breather. Nothing felt
Almost good enough, air could be exiting into the intake up the PCV circuit. You gotta plug all exits from the CC and I use a low-pressure gauge on the dipstick tube; but in times gone by, I would stick a hose on the dipstick tube and put the other end in my mouth
Popped rad cap. No bubbles.
Since the stat is closed, you might have to wait a long time for bubbles. Instead watch for any movement in the liquid, especially a rising liquid level, as, if air is entering the cooling system, it will push the coolant backwards thru the system, displacing it ever higher in the rad, and forcing it to overflow the open filler opening.
Removed exhaust pipe/muffler Hand over exhaust manifold. Nothing felt
probably overkill, but should be accurate. And a really good sign