Assembly line pumps with date codes are readily available on interweb.
My case was a bit different. I have an 06A with 396 and the switchover from the 065 the 811 casting occurred right before my car was built. However my engine was assembled in mid May. The pump that was on my car when I bought it was a long type Napa or some type of aftermarket unit. Being that the pump changeover from 065 to 811 occurred in April and my engine was assembled in mid May and car being built June 16, that left a pretty small date code window. I finally located a Tonawanda 811 pump dated 4/23/69. Took me over a year to find an 811 pump dated prior to my May 16 engine build date. That pump is the 811 pump seen in the CRG water pump report.