Well, a 180 ft one would be Gargantuan (or maybe even Colossal), but I'm not sure there's enough else to it other than just a nonstandard advancement for the dire eel. And the 180ft version just seems like an advanced version in the original text anyway. I'd lean toward skipping unless you think it's different enough.
Well, that's a nice use for the template to be sure, but I'm not sure it's worth a separate conversion. We have to let the other DMs have some fun.