There are three versions of the Aurelia oil pump - for the s. 1/2, s. 3/4, and s. 5/6. They differ in output, varying in the length (height) of their two gears. When we converted the s.2 engine from white metal to shell bearings, we used the s.5/6 oil pump, with no issues.
I think the s.3/4 pump is 24mm high, and the s. 5/6 pump is 30mm.
Never heard anyone say the s.4 pump was inadequate.