They will bolt up and work but if they are 87 - 93 they will not have the egr tube on the drivers side and your car might run bad, you will need the 94 - 95 headers to use the egr.
You can also do this if you want to attempt it, Take your stock header on the passenger side and cut the tube off and drill a hole and have it welded on to the new header.
A friend and me did this to his 95 mustang with the headers off my 91. I went to long tubes.
------------------
James Cox
nochevy@hotmail.com
1991 Mustang LX