it's missing the lower half... however that's ok because the part that's there is the one you want (it contains the pressure relief valve)

I would also get your mechanic to measure the clearances of the two pump drive gears (yours and this new one) and pick the best one, and make sure the new one is the same size!
(pump drive gears are the left two items of the three in the pic you linked)

If he doesnt know what he's doing, demand he does it for free