I would do as I do with my Studebakers:
EITHER..... use an oil such as Valvoline VR1 racing oil (I think?? it is synthetic, but irrelevant whether it is or isn't) which has the required amount of zinc and phosphorus as a "sacrificial coating" for at risk engine parts which should be about 50-50 ratio, and the concentration around 1400 ppm, as oils USED to have, and which is still needed for break-in off all new/re-done camshafts etc in particular, and all racing engines which have special needs (although Z & P are death to cat converters, so that is why it has disappeared from regular oil, especially since modern meturallurgy engines don't need it as such, as they don't have flat tappets etc),...
OR.... use a good quality regular oil--and a single grade such a 30 is a good thing for midsummer use--and add the product ZDDP which is formulated to add the right concentration of Zinc and Phosporus to make up the lack.
The cost is about the same. If you do it yourself, the cost for product is similar to getting an oil change done at an oil change place. You either pay +/- $5-6 a quart/litre plus taxes for something like VR1, or less for regular oil but about $8-10 per ZDDP container, so $30-$40 per change, taxes (and shipping if required) in. Cheap insurance for old flat tappet engines. Too little is bad, too much is just as bad for your engine, so DON'T double up.