I recently added a 1966 Galaxie 500 to the stable, which was for sure a want, and not a need.  Buying a car without seeing it in person since it was halfway across the country was not something I was too comfortable with at first with all of the scams nowadays, but after long conversations and lots of pictures and videos I decided to pull the trigger.  I had it shipped, it arrived, I was pleased.  The car is far from perfect, but that's supposed to be part of the fun, right?  Not knowing too much about older cars(also being just a brakes and oil guy) I had tried to get as much info from the owner as I could.  The car has 30,000 original miles and I was told a recent rebuild on the 390 big block.  Oil has always been a topic for any vehicle owner that will be argued until the end of time.  I run synthetic in everything I own and of course was wanting to change the Galaxie oil asap not knowing when it was done last or what was in it.  I swear that I can tell my vehicles start better and run better with it.  My late night can't sleep googling brought me to see something mentioning that it may have flat tappet cams and would thus need a zinc additive.  I had no idea that was a thing, although memory did bring me to thinking of seeing zinc bottles on auto store shelves in the past. Not knowing much about this rebuild I based my oil with zinc choice on assuming the cam is not a roller, thus is not as hardened metal and needs the zinc cushion.  Instead of using an additive I went with an oil that contains zinc and is manufactured just over the bridge from Duluth where I live.  I'm a fan of several brands but the availability of Amsoil and the "Prefered Customer" pricing has had me going that route lately.  So ZROD oil it is for this go around. 9 whole quarts because of the aftermarket oil pan.  Whether adding it to the oil or buying oil with it, I will always just lean to the cautious side and keep zinc in the engine at least until it's time to pull the cam to see it...and maybe beef her up more!