they do ok with pi gaskets. but i do understand. i had one leak at the water outlet. enjoy your stang. maybe with time you will change it tp PI or buy another 99-04. it is still the coolest model. 96-98.
The drilling part is easy. Get a tap set if you don't have one already. Drill the hole and thread with tap set on the right side of the aluminum crossover (I forget the exact size). Takes ~15 minutes and you're done.