The bolting pattern is different. The remanufactured pump does not come with new O-rings because you don't have to remove the rear case half from the connections. That is one of the benefits of the reman pumps. I have not needed new O-rings, but if you have them, it would be good to install them. I just use a little silicone on the block O-ring and none on the inlet or cross-tube O-rings (the cross tube has double O-rings). The gasket is obvioussly for the case mating surface, You will have to pry the old front case half from the rear. Try not to use any of the sealing surfaces. You will need to scrape the old gasket from the rear case half before installing the new one.
If you are installing a new CPS, it is best to do it when the water pump has been removed. This leaves a much cleaner path for the connector to be pulled up through the rear of the timing belt cover with a length of speaker wire.
