1968 340 oil capacity

I have used same Rotella 15W/40 with Lucas zddp for years without issues. Our climate is a little different north of the 49 lol
Thx i will add an extra 1/2 quart then mark stick with a File seems to be the majority answer.
I did add some ZDDP. I used to use 15/40 Rotella or plain old high mileage Quaker state 10/40 pretty hot here in AZ 10/40 should be fine Thx!