The 87-93 stock tubular headers will not work. I rebuilt my engine with P heads and cannot drive it yet because I have to save up for the headers. The passenger side was perfect, but on the driver side two of the plug boots are pressed against the header.
Check Jegs or Summit for the headers you need. In Jegs they are listed as 5.0L and GT40P specific headers but in Summit they are just listed for 5.0L's. Check out the part numbers though they are identical. Both catalogs list them for $239.
Good luck,
Joey