You want the genuine Porsche pump. It's made by Pierberg, and you can get it for a lot less if you buy it in a Pierberg box instead of a Porsche box. Only difference will be that the little triangle with the P inside might be ground off with a dremel on the Pierberg one. Identical pump though, right down to the Porsche part number in the casting...
If it's too late and you have already ordered a pump I'll post this here anyway for others to see...
When changing the pump, there's one bolt that is especially hard to access. It's the lower right bolt (looking at the pump from the front). I used a 10mm socket that had a flexy joint built into it. Pay attention to where each bolt came from. I think the problem child bolt is a bit longer than the others.
Lastly, do not over-tighten the bolts. I think you torque them to some ridiculously low value like 8 ft-lbs.