What year did they put the 3rd bolt on the starter you had to go in above the starter with a short socket and a long extension? If I remember it correctly, a 18" long extension (a couple shorter extensions will work, but not as well as a single long one) will get you past the exhaust pipe so you can use a ratchet. Without the long extension, the ratchet ends up right at the exhaust pipe and there isn't enough room to swing the ratchet.
That starter bolt uses the same socket as the two on the front. I suggest you put at least one of the front bolts back in the starter to hold it in place until you have the back bolt out, or the starter may fall and hit you on the head. Once all the bolts are out, the starters tend to fall right out, but you need to turn it just right to get the wires off the starter, then you need to twist it just right to get it out of the hole. I was always amazed the starter would fall out, but once you removed the wires, you have to flip it a dozen different way to get it out of the hole its in.
Good luck. Gene