Harry,
We had quite an extensive discussion on this forum a year or two ago, and you might be able to dig that up for a complete rendition. Basically synthetics are going to rate higher than non-syns in every category of performance, but in addition what's critical is to make sure sure you are getting an oil that is high in "ZDDP". That's the protective zinc additive needed to protect the valve train of any flat-tappet engine. This is not a good choice for later cars that have catalytic converters, however, as the zinc will wreck it by "poisoning" the catalyst - coating it so it no longer works.
There are many brands to choose from, and we may have our personal favorites, but Royal Purple is one brand with high ZDDP, and Hemmings also offers a good ZDDP oil.
Keith Boonstra
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