Oh you already have a used one, I would say go with that. The guy I bought my car from has used junked ones several times with success, usual cost around $20. I found a link to one car he helped with the build on, you can see the pump in the pic-

300SD extra pump install

The reason I was suggesting a new one was when I was at two junkyards in CA the owners told me if they were doing what I was doing they would just buy a new pump over the internet.