Not sure about 455G. I can tell you that on a 450C it is easier to pull the engine if you are going to drop the pan. If you don't have a tech manual the best thing I can tell you is to drop the belly pan and crawl under to see what things look like to get the pan down.
On 450C you can have the whole engine out in a little over two hours. Get loader blocked up high in the air, disconnect lines from hydraulic pump on front of engine, disconnect fuel lines and electrical. Remove radiator housing assembly with radiator, hook hoist to engine. Unbolt from clutch housing which will stay in place. Wiggle it and "walah" roll it out.
I seems to me that there should be enough room to drop the pan down once you get the skid pan off the bottom which is pretty easy. Having machine up on blocks a good twelve inches will help to so you have some room to roll under on a creeper.