An 11 bolt water pump would only fit a timing cover '69 and newer.

Design of timing tab changed over the years. This may affect the alignment of indicated TDC vs. true TDC if the balancer ring has slipped or if the cover's tab is in a different location relative to the year of the balancer.

I make my own TDC mark for reference for initial distributor installation (using physical TDC), but I set the timing based on the way the car runs.