If you use the proper oils for the engine in question, the addition of uncertain amounts of ANY additive is the equivalent of playing roulette - you have no control over the outcome.
Use an oil formulated for the engine in question and that's all it will require - and today's fleet and marine oils will run longer, cleaner, faster in your engine than that of 43 years ago.
I build lots of Olds 455's and GM 454's from the early 70's - every one runs Pennzoil LongLife 15W-40 and has zero lube problems - both flat tappet and roller cammed. Know that I am partial to dumping in a quart of Joe Gibbs Driven HR-4 along with 7 quarts of LongLife in a marine engine oil change at 100+ hours - the equivalent of ~7,000 miles. My big engines run a Milodon 8 quart pan. The STS and trucks (all roller cammed) run a modern synthetic oil - 5W-30 in the car, 5W-20 in the trucks.