Not a jerk, at all...I'm actually a really nice guy.
And...not to sound "cocky", as you put it...I know exactly what I'm doing and you have no idea what you've gotten yourself into. I have a very extensive knowledge of moray species and what you have is a monster.
Adult morays are alot different than juveniles. Keep adults happy with top water quality, plenty of rock work, fed on a regular basis and they're happy just where they are. I've had both of my Morays, as well as others in the past, in tanks with no tops...for years (not weeks, not months...years) and have never had one attempt at escaping.
You say your other fish and ray are "doing just fine" but please, dont be afraid to post here on the board and let us know when that Green eats them. It's not a matter of IF...it's only a question of WHEN.
The 300gal. will not fit into my basement...you are correct. That doesnt mean I dont have any place to set it up. And, as far as the pond...you build those on site.
Hopefully, since I'm a "jerk" and even if you needed to, you wouldnt send the Green to me, I just hope that you've thought far enough ahead and have enough room in your house for a massive tank, for the Green alone...or, you've got someone in mind that can give it a proper home.