I just completed this job today with the help of a friend, and it was fairly easy except the getting the filler tube out and back in part. On my 2000 GT, the tube was so rusted out at the bottom that I was able to bend it by hand which helped get it out, but the plastic tip still broke off in the tank on my last pull. Then getting the new one in was a b*$%# as well, but loosening the tank straps helped so I could move the tank about a quarter inch to slide the new pipe in.
I checked at the dealership and the pipe assembly (part # 3R3Z-9034-AA) was almost $200 from them! The seal (# 2R3Z-9072-AA) was then $25. But I found the assembly on ebay thru Tasca Ford and then called them about the seal, I got the assembly for 91 and the seal for 13 and shipping for 14 bucks! Check them out online also: www.tascafordparts.com
Oh, and I didn't see the need to remove the RR wheel, but if you could lower your tailpipe, that would give you more room to maneuver under there. Then again laying on the ground trying to do all this wasn't the best, so if you can hoist the car, I'd suggest that.