The first two camaro ZL1's came with the aluminum water pump that were natural aluminum finish casting #3968811. This pump looked exactly like the cast iron pump but it was aluminum... They only used it on the first two or so cars before they noticed that the bearing was moving in the housing so they went to the cast iron pump.. It explains it on page 176 in The 1969 Camaro Reference Book From A to Z by John Hooper.. It also says they used the short aluminum pump like the corvette pump as well... Here is a part # list on the ZL1 cars...
http://www.copo.com/ZL1-Parts-Listing.htm Hope this helps...
