Run the tank low if you can for convenience, if the fuel level is above the hole it will pour out on you and that is never fun. You can change it with the tank in with no problem, and replace the gasket with a new one whether it comes with one or not, you don't want to do it twice. YOU will have the easiest route if you can jack the car up and suspend the rear end, it provides you with extra working room, I would also plan to replace the hoses and go under the car with a sharp knife and just cut throught the old ones, have 5/16 and 1/4 inch line on hand. new worm clamps unless you are doing the crimp style clamps.