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					Originally Posted by zrayr  ^^^^^ this ! 
I use/used in all all small & big blocks.  Never any oiling issues.  There just isn't much of an argument for not using a quality synthetic  in these vintage engines. The friction reducing properties are well known and throughly documented. Simply put, your engine will just last longer. 
 
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 I believe there are several arguments.  Some were mentioned in this tread already by knowledgeable engine builders.