The dipstick is a bigger liar than most fishermen that I have met.
Drain both front & rear sumps, change the filter and add 4 quarts oil. Start the engine and let it idle 2 minutes or so. Shut it off, wait 2 minutes for the oil to drain back into the pan. Pull the dipstick out, wipe it off and stick it back in. Pull it out again and take note of the oil level. I marked the dipstick with a scratch from a file at the 4 quart level.
Add the 5th quart, start the engine and let it idle 2 minutes or so. Shut it off, wait 2 minutes for the oil to drain back into the pan. Pull the dipstick out, wipe it off and stick it back in. Pull it out again and take note of the oil level; it won't be anywhere near the factory full marks. I marked the dipstick with a scratch from a file at the 5 quart level, which is about 1" above the factory full mark.