Countryhousedr,
Robert Hensel\'s 1996 article on Chevrolet engine colors shows that in some years the 261 engine might have been yellow (this is the same information at the link given by red58, above). I have seen a yellow 261 Jobmaster engine in a tow truck and the owner (Bob Adler, an expert) thought the yellow color might have been original.
My 1960 261 engine had remnants of the green color that is very close to paint that Jim Carter sells for all 261s.
JC's olive-green PT117 is listed for 39-48 GMC engines.
Tim
