The P heads require specific headers to clear the spark plugs so make sure the ones you get will fit. I would also recommend replacing your timing chain while you’re in there. A set a ARP head bolts would be a good thing too.
Changing heads is a time consuming job but not hard. The biggest thing is to get the deck of the block extremely clean and the mating surfaces of the heads. Don’t use a Scotch bright pad or anything else that could leave stuff that would end up in your engine.
I like to use the Explorer intake gaskets the have the silicone China rail gaskets. As I’ve found them to not leak and last a long time.
Use the proper RTV gasket maker. Permitex makes RTV for parts that come into contact with oil (black) and coolant (gray). Also make sure you use thread sealer on the head bolts that go into the water jackets.
One other tip. Go to the hardware store and get 4 bolts that are the same thread and size as the lower intake bolts and above 2 1/2 -3” long. Cut the heads off of them. When you go to install the lower intake thread them into the heads for a guide. They will guarantee that your lower intake gaskets doesn’t slip and make your life much easier.
Let us know if you have any specific questions.