Is it too nitty to say that calling a 25x pre with 6
7
makes you, and not Villain, the maniac?
You're pretty close a dog 60% of the time, and you need a pretty specific flop to continue, especially since both of you know what he has (assuming he's the only honest player left in poker, as you contend). That seems like it would make it difficult to get more money in post if you hit your big-time flop.
It'd be a lot different if you had other callers in there, but HU? Probably not.
67s is a hand you use to stack tags, not maniacs. Use the topshelf for that.