leon63

This may be a dumb question, but have you removed the starter? It is sort of a pain to remove the top bolt. Be sure to undo battery cables forst. Also, the O2 sensors are a pain to unplug, it takes some time... If the mfld nuts are not too rounded, I would invest in a good 15mm deep socket, and first spray with good penetrating oil. I put shorty headers on my 02 GT - I know what you are going through.

leon63

Another idea... Someone else in a recent related post described a Craftsman socket that "bites" into the rounded nut for removal. I snapped off two of the manifold bolts when I was removing the h-pipe - not too fun...