Burn regular gasoline in your old cars. You don't have to use higher octane than 87 and you don'e have to worry about the 10% ethanol. The engine won't mind at all. Your engine oil 10w-30 will take care of all the lubrication needs. A little MM will not hurt, if you insist on adding something.
All the other stuff is mere "snake oil" and is for gullible people who just can't resist on tinkering and screwing around with an already good running engine. resist the temptation to visit the "add to" shelves at your local parts store. Your engine will thank you and your pocketbook will be heavier.
My two cents worth. And, another thing, the lighter the oil sufficient for your engine, transmission and differential, the better. Not, conversely, the heaviest
ones. Well, that's about three cents, now.
Charlie