I stand corrected. UN is for a 396/375 w/manual trans. UO 396/375 w/TH400. ZE - 396/375 w/TH400. ZD - 396/375 w/manual trans. My source is observation of different cars and comparing finds with other Camaro folks. As far as I know, there is no factory ID info on these codes
. UN & ZD are for same app., but why different tags? Maybe a production/engineering change at some point. I am interested to know what is the two letter embossed raised code, stamped on the the right side tank of your radiator just below the "fill" line?