ALTHOUGH Lots of people on here agree its in the valve train, to me it sounds exactly like my 1992 when I bought it, the owner did headgaskets and then started to make this noise, it brought back some bad memorys.
mine ended up being the number 3 cyl rod knocking.
1st remove the super charger belt, eleminate the supercharger.
then i would let it run, and carefully pull each spark plug wire off one by one, basicaly do a cyl cut out test. when you pull the plug to the cyl that is making the noise it will go away or get alot quieter (IF ITS A ROD BEARING). if noise stays then remove the intake and take a peek.
we chased that exact noise around on my car (bought it because I thought it was lifters also) and turned out to be rod knock.