What type of oil to use in a Skyliner

Hi,
Over the years I have heard many different suggestions as to what type of oil to use in a classic car. I have heard some people say straight 30 weight. Some say 10W40. I have heard 20W50. A couple of people have said straight 40 weight. I was just curious what others use?
I have used a blend of 10W40 and 20W50. I also add a zinc additive in as well.
Thanks

20/50 is what I have always used. Many different cars ranging from 55-70.
The 76 racing oil has zinc added.