Looking at it again that may be a 6cyl pump pulley. Early Holden V8 is much shorter from the face of the pulley to the groove. Here are some:

http://www.ebay.com.au/itm/holden-25...item27d0b098b3
http://www.ebay.com.au/itm/HOLDEN-25...item19d0a0428f
http://www.ebay.com.au/itm/HOLDEN-25...item19d60eab23

With the bigger bearing (longer) pump used later the pulley is longer. Here are some:

http://www.ebay.com.au/itm/HOLDEN-25...item1c26b46f7f
http://www.ebay.com.au/itm/HOLDEN-V8...item4170ac1980

I'd measure the "height" of your pulley and get someone to measure their V8 one. I won't be near one until Wed morning.

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Quote Originally Posted by ambientgoat View Post
[MENTION=2]Blocker[/MENTION] just came and borrowed a square pulley for trail fit.
Given the parts manual gives different parts numbers for the water pump pulley, I'd have a guess that the square pulley is correct for power steer cars and the round is correct for those without. Rather than it being an early/late thing.
It is def early and late. The bigger bearing pumps were introduced late in 1978 or thereabouts, and this pushed the pulley face further out, meaning the pulley is "taller".