regarding full synthetic oil

Not enough information to give you meaningful advice.

The most important part is the style of camshaft, if it has a flat tappet cam the oil needs to have a fairly high zinc content so the lifters and cam lobes stay happy. But if it’s got a roller cam upgrade you don’t need the zinc.

Next up is if the engine is original or rebuilt. If it’s all original with 60’s tolerances you don’t want to run thinner oil, you could lose oil pressure and pick up leaks. But if the engine has been rebuilt with more modern clearances then you can run more typical modern engine oil weights.

Just saying it’s a 440 and it needs 20-50w is nowhere near the whole story.