Any name brand engine oil should be good for the multi, and is no doubt miles ahead of whatever crud the army was buying in bulk back in the day. Im a big fan of Napa's house brand, its made by Valvoline and a good price. Zinc has been a concern for a long time, but I feel thats really a bigger issue for engines with high valvetrain/ spring loads. In any event, as I mentioned above, my own opinion is that modern oils are so much better all around that the specific loss of zinc isn't a catastrophic issue.
The youtube channel ProjectFarm did some testing a while back with vintage oil vs cheap modern stuff, and the difference was astounding. the new stuff was miles ahead.
As for fuel, Im a strong believer in 2 stroke oil. Ive been running it in mechanically injected Cummins for over 10 years and believe it to be excellent, especially for the price point. I've heard some guys champion trans fluid over the years, but most of that stuff is synthetic now, which doesn't burn as good, and has lots of other additives in it for clutchpack slippage control and all that. Two stroke oil is designed to be a consumable lubricant, and its very good at it. Come to think of it, I think ProjectFarm tested that too!