Honestly, the maximum size for a lot of eels is greatly over stated. I have seen Green morays (Gymnothorax funebris) kept healthy and happy in 240's and 300's. We have one in a 200g holding tank in our bio center ( Im a marine biology major at UWM), and hes got to be at least 4 feet, maybe even 5- and he does nothing but look out of his tunnel and eat when we feed him.
Think about it this way: how active are these fish really? They might come out when your asleep and the lights are out, take a few laps, and hunt for mostly non existent food, and then return to the safety of their burrow. I currently have a 2 1/3 foot White Eye'd (Gymnothorax thyrsoideus) in a standard 4 foot 90'g tank, and im quite positive he would do fine in a 55 if i had to. (with a sump for additional water volume.)
As long as you have proper water flow and keep your nutrients under raps, it should do fine for many years in that sized tank, but i do agree a 240g or a 300g would be a good size to upgrade too.
Just my .02