Do not have to have a tap and tap the holes, the bolts will do it, but start threading with the bolts with the water pump out is alot easier to start them straight.
My alternator bolt hole in the water pump was to tight and had to do the same and thread it in there also.
So 4 holes to thread.
Have the new water pump sitting in front of you and as you take one out set it in the hole of the new water pump all the way around to make it easier to keep the bolts in order and also makes sure you have all the bolts out, then when old water pump is out set it beside new water pump and transfer bolts straight over, then when new water pump goes in your bolts are in order.