Northstar is braver than myself. I would not attempt to move a 55 with gravel let alone any water. I've done his approach with 20's and smaller but wouldn't risk it on a tank as long and thin as a 55.
I would get your buckets, tubs, siphon, a buddy, etc on hand first because the faster you complete the move the less stressfull it is for the fish. Fill the container that will temporarily hold the fish first as the water will be cleaner before you disturb anything. Next fill any reserve water you want, depending on how suitable your tap water is this amount will vary. Next drain and discard water until the tank is about 1/3 full. Now you can more easily remove the fish. Remove your plants, decorations, etc. Drain the remaining water and discard remove most of the gravel and set aside. If the tank has been running a while the gravel will be quite dirty but be cautious on cleaning this as it is home to much of the bacteria you need to keep alive to avoid having to cycle the tank. If your maintenance hasn't been the best you may gently rinse the worst of it with non-chlorinated water of the same temperature. Now the tank can be easily moved and reset accordingly. Once reset, go easy on the feedings (if at all) for a few days to be sure the tank cycle hasn't been broken, and test your water daily during this time.
Good luck.