You should just buy oil that has the required amount of ZDDP in it. There are many brands that will do fine. My rule is to get something that is available everywhere. So I use Valvoline Racing oil. Any Wal - Mart has it, as do most auto part stores. Your old flat tappet performance engine from the 1970’s needs it all the time to prevent damage.
Your glove box book has recommended oil types for various temperatures. 5W-30 is not one of the listed oils. 10W-30 is a typical winter oil grade.