I believe that the original logos were painted onto the valve cover. The style changed with the engine.
Here is info about the ThriftMaster 235 logo for my '54 3104 that I regrettably sold. Earlier logos were script.
I traced and tweaked a decal that I bought from the major AD Chevy truck suppliers. Then a vinyl sign maker cut the traced logo from yellow vinyl sign material. I applied it using a placement diagram in the Assembly Manual. It looks great. You have to look hard to tell that it is a decal.
I believe that the vinyl sign shop still has the file to cut a ThrifMaster235 decal. Cost is probably around $20. Contact me.
I can send the full-size ThrifMaster 235 pattern if you want.
I recently found a removable stencil material that you can use to paint the logo. Seals tightly around the openings and removes cleanly. Cut with an Xacto knife. Remove the backing. Rattle-can spray paint, or dab the paint on with a foam brush. The stencil material is Oracal® 813 Adhesive Stencil Film. I think that it is discontinued, but similar film is available.
I can send the full-size ThrifMaster 235 pattern if you want.
Lonnie
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