Oil capacity for magnum with LA pan

You're going about it backwards.

Drain oil, replace plug. Add 4 quarts. Dip your Magnum stick (snicker).

This is "Add". Mark with little pin drill, scratch marks, whatev.

Add a Quart. Wipe n' dip. This is "full".
Mark accordingly.

For me, I punched the pin outta the magnum stick, and shortened/drilled accordingly to make my longer-but-factory marks move up to where I needed them.