Possibly some useful info to answer your question.
This page from the
1929-54 Chevy Master Parts Catalog lists the "stud", "bushing" and "2 washers" (Parts Group 3.582) for the engine mounted accelerator bell crank pivot. All those are 1954 Commercial Truck with A.T. (Hydra-Matic) specific parts.
A snapshot below from the 1947-54 Reproduction FAM (Sect 7 Sheet 3.01) shows in "VIEW A" that those washers go on either side of the bell crank. Haven't found anything to indicate that the stud used a washer to secure to the engine block itself.
Also attached is a better picture from the 1954 Shop Manual (page 7-41) of the Hydra-Matic accelerator & transmission controls in case it could help out in anyway.
Let us know how your "fix" turns out.

Dan