Nailhead water pump question

[Jolly_John]

I sold a water pump (the correct pump) for a 1963 Riviera with 401 engine to a hobby guy in Australia. Upon receipt, he has informed me that the pump I sent is too wide to fit the timing cover of the engine in his Riv.

However, he and I both now suspect that his timing cover was changed over the years and may have come from an earlier nailhead. It seems possible that the engine is indeed a 401, but that the timing cover might have worn through, and was replaced with whatever nailhead cover was available there.

Does this make sense to any of you....and can you shed some light on when the nailhead timing covers may have changed in design? Both the fellow in Australia and I thank you! John<!-- google_ad_section_end -->