Blocker just measured that square edge one for me at 40mm front to back. 308 with shortnose pump
Other 308 I has the long nose pump with a square edge pulley at 60mm.

Different people doing measurements, so I can't ensure we're measureing the same. But I'm guessing there are different length square and round pulleys.

Here is a photo of the motor the square pulley came off, now with round pulley and lining up with nothing.
photo.jpg