Timing Curve on 360 in an RV

Anyone know a clever way to confirm I’m at 12 degrees BTDC on the compression stroke of cylinder #1 without taking the valve cover off?

Last time I hand cranked the engine with a finger over the spark plug hole until I felt pressure, dialed it to 12/before on the markings on my balancer, and then used a screw driver to check it was near the top.

Turn it to 12 on the balancer and then take the fist) dist cap off and see if the rotor is pointing at #1 terminal. If not, you're on the exhaust stroke.

If you're talking about confirming the balancer ring hasn't slipped, you'll need a piston stop.