a bad water pump should not make a loud thumping noise under load, that sounds like something else causing the noise. but if the pump is leaking at the weep hole it needs replaced.
crank pulley doesnt need to come off for water pump change. also fan clutch doesnt need replaced just because water pump went bad, if the clutch is still working its fine to leave it alone.
i suggest getting a repair manual, it will tell you the torque specs etc. i use a thin layer of sealer on both sides of both gaskets, ultra grey or ultra black permatex is good stuff, a thin bead spread out with your fingers then follow instructions on the tube for curing. the bolts can be tightened in an even pattern, no specific sequence, i do the top bolt, then bottom, then left/right sides, then the rest criss crossed kind of like a lug nut pattern. once its together & dried start up & check for leaks. then after a few heat cycles snug the bolts again, you can get to most of them with a little creativity with the wrench. also good idea to use anti sieze on the bolts going into the aluminum timing cover. its a pretty basic job & easy to do if you follow the manual.
also, pontiac pumps need to be clearanced to the divider plate to cool properly. when assembled on the bench the impeller should be as close to the divider plate as possible, like .010 clearance. if needed gently hammer or bend the divider in then test fit untill there is a tight clearance. if its too big of a gap it wont work right & you can have overheating issues.
