Perkins 4.108 Raw Water Pump Drive Tab

[OldRover]

Can anyone explain how the drive tab is mounted into the fuel injector pump hub? The long story is that I am replacing my 4.108 and was working with a rebuilder who provided a long block (basically a standard Perkins minus the marine specific stuff). I pulled the oil pan with siphon, front cover with pump mount and drive hole, exhaust manifold/heat exchanger, bell housing... from the original and am adding to the rebuilt block. Due to a broken finger I shipped the core back to the rebuilder with a couple of minor components left on which he was nice enough to pull and send back to me. One of which is the drive tab for the sea water pump. It appears to be a press fit into the front of the fuel injector pump hub. Is there a bushing between the hub and drive tab? It seems that I do not have sufficient clearance to press the drive tab in. Is there a specific procedure? I assume that this must be done with pump and hub mount so the circlip can be in place with the drive tab pressed in after the circlip. Is this correct?
Thanks in advance.