Not sure how much oil should be in my engine
 

I have a 1953 Super 88. I've only had it a couple of months. I bought it from a woman who inherited it and didn't know anything about it. Anyway, I just got it running. I have been researching the car to see exactly what I have. It turns out my engine block number is 8A225843 indicating it is from a 1950 Olds. The heads have a 7 on them indicating they come from a 1954 303 cubic inch engine and the carburetor is a Rochester 7007221 4GC from a 1956 Olds. My question is how much oil should I have put in after changing the oil and filter. I put in six quarts. The oil dipstick shows the full level and is marked at 5 quarts. So my oil level is always about a half an inch above the full mark on the dipstick. Did the 1950 303 engine only take 5 quarts with a filter change and I am now overfilling the engine? I can't find any information on how much oil a 1950 303 cubic inch engine should hold. Thank you for any help given in this.