The dipstick is wrong, heck its so old maybe a different one was swap years back, maybe the diptick tube when replaced on a rebuild was not driven in far enough..maybe the tube is the wrong length--who cares. On every engine I had I change the oil and filter, give it 5 quarts, run it and once off for an hour take a file and scribe a line right where the oil level is on the dipstick. That is now your full max level
The afermaket tubes never seem to be right on