What is Mercery recommendations oil capacity for a1999 502 gen VI EFI MAG with stock oil pan and remote filter?

It should be 7 quarts if you drain the oil out of a hose on the bottom of the pan. If you pump it out the dipstick it may only hold 6 to 6 1/2.

I pump my 1997 502 mpi mags out of the dipstick and they take about 6 1/2 quarts to fill.

If all the old oil is out, its 8qts.

You need to fire the engine and circulate the oil after refilling, then recheck the level with the boat at the same angle as the way it sits in the water.