the starter top bolt is a pain to get out. there is three bolts facing the rear of the car( let me make this clear.the heads of the bolts the part you put a socket on faces the front of the car by faces the rear i meant thats the way they screw in). the bottom one and the middle one are easy. the top one will have you hoping dick cheney takes whoever thought it was a good idea to put that top bolt there on a hunting trip.
the way i do the top one is with a swivel socket and and a LONG extension feed in between the k member right under and to the outside of the exhaust manifold. you have one hand holding the socket on and the other hand all the way near the a/c compressor. i have only done one with the h-pipe off. never attempted to do it with the h-pipe on the car.
After trying all kinds of extensions and wobbly combinations, thinking it was harder than it actually was, a small 1/4 drive ratchet and shallow socket was able to reach the top one. It was a HUGE pain in the ass until I realized the eaziest solution was the right one.
p.s. I did install my starter before the x pipe was on so I dont know how badly your down pipe will complicate things.