If you have any concern about your oil pump and do not know what to look for, I would suggest taking it to your machine shop and let them take a look at it for you. It would also depend on if your rebuilding because there was a bunch of trash that ruined your bearings or your just rebuild to freshen things up. Like one of the previous post said it all depends on what it looks like. I used to rebuild Porsche engines and some of this oil pumps could push $3000. You can do a lot of checking, cleaning and repairing for $3000!
Have someone who rebuilds engines for a living look at it and see if it's worn. If it looks ok to them have them do some measuring and see if the shafts are worn or the bores for the shafts are worn. A good machine shop will charge about $15 to check it out and then you will know for sure. Water pump should be replaced no matter what for $30!
