Just to throw a monkey wrench in the mix on the alternator bracket, the LIFE photo of the engine assembly plant clearly shows orange brackets. These may not be truck engines, but at least SOME smallblocks got orange brackets... And I believe the year on the photo was '59.
http://www.camaros.org/images/assemb...ly-engines.jpg
But the '68 engines brochure shows black...
http://paintref.com/graphics/brochur...vpickup_11.jpg
Rg