So, finally pulled my pump to look for this date code and still couldn't find one. Then stripped all the paint off and discovered an AMC logo stamped into it.
It does have the correct pulley as per below [looks like original phosphate under the black paint.]
So, I'm now on the lookout for a pump that has a reasonably correct date code to suit a 12c 68.
Any ideas what date would be correct?
Maybe others could chime in with what their build dates v. pump dates are.
These housings look good http://www.ecklerscorvette.com/1969-corvette-power-steering-reservoir.html
though it appears that the 'conning tower' is internal to the cover, not external like originals.