Use any brand 50 W (detergent or non-detergent) oil in an oil bath air cleaner.

The oil catches the dust/dirt.
The oil weight allows the oil to migrate into the mesh/element, but supposedly not enough to get sucked into the carburetor.

no need to be synthetic
no need to have any additives

Tim
1954Advance-Design.com
1954 3106 Carryall Suburban
1954 3104 5-window pickup w/Hydra-Matic
The 216 and early 235 engines are not "splash oilers" -- this is a splash oiler.