Is it similar to any other fish you've cleaned?
(love fresh and saltwater fish but never dealt with an ocean sunfish).
Similar? No, not at all, it's an alien. Well, it's flat-ish. Mola Mola has no bony skeleton to worry about, but the skin is a thick, tough collagen, and the meat is gelatinous. Don't even think about the organs because they're full of parasites. Probably easier to see it. Dude doesn't use much artistic grace but you'll get the idea of its body and meat:
Opah (known as sunfish or moonfish depending on the region) is structured more like a traditional flatfish, minus the spine running down the center separating the filets. It's really easy to filet and has a ton of different cuts, like a cow almost.
I dealt with one sunfish, and this was do to very unique circumstances. Stick to Opah.