Block offs go between the front bumper and radiator core support. Fills in that big hole on each side of the hood latch.
Underside baffle isn't as important but definitely would help.

Water pumps are hit and miss finding a cast impeller, I've run both without issue though. Just make sure whatever you get doesn't scrub the divider plate. Once you pull the pump make sure the plate is in good shape, also you'll see two tubes that go from the divider into the Timing cover, check them for condition and that their rubber O ring gaskets are in place.

Simple stuff, but if you haven't worked on a Pontiac it's just one more quirky thing about them.