Rotella 10w-40 ( or other diesel rated oil ) is closest to what the formulations were when your car was manufactured. you may want to include a zinc additive.
the 'problem' with modern automotive oils is catalytic convertors. zinc and lead and a lot of the other additives that used to be in the formula clog the convertors up.
your car never had a convertor.
the 1952 Shop manual should apply to your car. the 320 was in production for decades and the 263 is an uprated version of the 248.
http://www.teambuick.com/reference/l...shop/index.php
The way to crush the bourgeoisie is to grind them between the millstones of taxation and inflation.
Vladimir Lenin
Government schooling is about "the perfect organization of the hive."
H.H. Goddard, Human Efficiency (1920)
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