IMO... the need for high zinc oils for a stock cam is not necessary. I good lubricating oil is the best for you. And the lifters in the /6 are pretty hard.
With an older engine and oil pump. the pump may be worn and will have a harder time pulling up a heavier oil. So I would stick with no heavier than 10W30 and consider a 5W20 for your /6.
The way zinc works, having an excess does nothing unless you run your oil forever and ever. I would strongly suggest anyone wanting to learn more about oil and zinc read this and for the OP to select one of the higher ranked oils in this list. It shows how some zinc additive packages actually reduce the lubricating properties of many oils. This is a long read so be prepared to sit for a while:
https://540ratblog.wordpress.com/2013/06/20/motor-oil-wear-test-ranking/
