I have a Leiarius marmoratus is about a year old and already 15". I posted on your other thread and I would vote no in the 180 for the long term, for a grow out yes. They max out over 2 feet and the 180 does not have a big enough footprint. As far a temperment, mine shows no aggression at all, eats anything that hits the water and will let me pet it occassionally.
Its a no go for a 180. I have two at the moment and they are both around 18". I had one a year ago that died at around 26" and was a very active fish prior to his death. The thing is that they are very calm and dont move much during the day. However at night, they are constantly swimming and moving about the tank. A 180 gallon footprint is simply not enough for that fish to adequately move around.
I've never heard of them getting over 24". The largest I've seen in person was probably about 20-22", but I agree that a 26" cat would be too large for a 180.
I may have added a few inches to the total because of a little extra on the tail streamers. The body, not including whiskers (which are a foot long by themselves) or tail streamers, was probably around 23".