You must have a later pump then Blocker, has to be with that pulley. Did it have 2 x gaskets at the back and a sandwich plate, with a barrel impeller?
If it is the longer pump trial fit it once the car is finished as it may have fan to shroud issues.

Goat, 74 part numbers are HK era, so maybe they used a wierdo pulley on some HJ? I'm certain mine has the round one and that is all i've ever seen on earlier red motors. I still reckon that rounded pulley can't be a 253/308 red one as those are shallower than the later square edged ones not deeper like Blocker found. Maybe the square edge one you loaned Blocker is one of the earlier ones from HK era and are the same depth as the normal rounded ones. It doesn't look as deep as it should, but may just be camera angles? Will be interesting to find out the answers. I'll measure some when I get home to satisfy my curiousity.