[42merc]

I had the same engine / pan / stick combo in my '40. 5 quarts registered low on the stick.
On a trip to Colorado, (from Michigan) with the oil filled to the full mark on the dipstick, I was using a quart of oil about every 500 miles. This was with a fresh & sound engine well broken in.
On my return trip I let the oil stay at the add mark (about a quart low) & used not a drop of oil for 1200 miles.
What I'm saying is - 6 quarts in a flathead is too much oil. If your are just puttin' around town it doesn't matter. But at speed, 60 to 70 mph plus it made a difference. The car was OD equipped to allow these speeds.