a green moray in a 150 is not ideal long term...I'd go with a smaller species, like G. vicinus (purplemouth moray) if you want something with the overall look of the green. They also come from the same region assuming you mean G. funebris.
For a 55 there are a few species you can keep in tank that size, like G. tile, G. richardsoni, or some of the smaller Echidna morays. Minimum tank size for some species is debateable, as various sources will vary on what would be minimum for something like a snowflake eel.