You could just look for an early 1996 explorer and see if it has standard GT-40 heads.
Will save you in cost over the P heads as you can use any standard Mustang header.
Still need to upgrade the springs
Will the GT-40 NOT P heads have EGR and AIR ports that will work with the stock Mustang's systems? I know the later Explorer manifolds do not have the EGR passage in the middle.