Really, I think you should re-think your strategy here. If you haven't already got the fish then you have options. You can still get it drilled to enable a sump. Alternatively, you could get a sypon box - you can get quite a lot of water down those things.
A sump will give you two key (essential) advantages:
1. It offers the opportunity to increase the volume of water in the tank significantly. Morays are less active, so as such you can use a smaller display - but they are none the less big animals. At 24" long and 1" in girth, that is about 19 cubic inches of flesh. At 30" and 1.5" girth = 53, at 36 x 2 = 113 ..... so a 50% increase in length will be a 5 times increase in body weight ...... that's very rough figures obvisouly but think of it this way ..... thats about the same body mass as 12 x 4" yellow tangs ...... and the moray is predator so is messier..... and will grow well past 36". So water volume is going to be of huge importance both intially and very quickly after.
2. With a sump, you can get a decent skimmer. It needs to be really oversized.You might actually benefit more from two smaller skimmers as it will continue to skim on the days that you don't feed - and it will cope with the surge after a big feed.
In all honesty - to attempt this fish in a 75 gal tank, with anything else, is fools folly. It is a case of just because you can do something it doesn't mean you should. Big sump, big skimmer, and high capacity filter is a must - in my view.
