One thing you might want to do is go to hardware store and get you two bolts that are way longer than the ones in the pump. Cut the heads off and you can use them to help keep the gasket in place and also slide the pump on over them and get the other bolts started then remove the studs and put correct bolts in. I do this when putting a transmission in also. Cut off two bolts in bottom two holes and you can slide the transmission right in.
Also be sure to put sealer on the threads of bolts that go into the water jacket. Pump usually has some instructions in the box.
Also take it easy getting old bolts out can be rusty and snap off. Soak them couple days with penetrating oil for sure. If you can get a hammer in there and hit the bolt on the head that helps break the rust loose also. One of the members is in a jam now because of a broken water pump bolt or bolts that he then broke a tap off in the hole. Can cause you to have to pull engine out to get the broken bolts out.
You should run a tap in the threads of all the holes to clean them out and when you go back put anti seize on the threads. Use a pipe cleaner or small dia. screw driver and put the anti seize in the tapped hole, just a little and put the sealer on the bolt threads. Bolts not in water jacket do not need sealer but use anti seize on all.
When using a tap only use a tap handle and never try to use a wrench to turn the tap you will break it. Go slow and do not force it. Turn tap in one turn and back up a little then a turn and back up to keep it clear.
Here is a pic of the anti seize can get at any parts house.
If you get a tap get a two flute plug not a 4 flute. All you are doing is cleaning the threads not cutting so should screw in easily. Blow the holes out with compressed air.