Cool so 180 gallons then
There are a couple of safer options - though as with all cichlids nothing is set in stone, it may be worth having the 3 foot set up as a reserve tank if possible? Maybe keep a sponge filter in the big tank incase you need to move someone around. For me I would try this given your water.
1. Jack dempsey
1. Black belt
1. Red terror - which type of Red Terror is this Midas or Festae?
The JD may be out competed in a couple of respects but could potentially hold its own. Tank mates are a bit tricky, I'd like to suggest some Central American tetras like Astynax and Roiboides as some of them get to a really good size but I think they will be hard to track down in Australia as I know you have import restrictions. Some of the big barbs could work like Spanner Barbs of Filiament Barbs, Giant Danios might do well too but might not be big enough. Im tempted to say keep the bottom of the tank clear but there are some nice fish that could work like big Syno catfish that are used to living with African Cichlids. Synodontis Decorus is really nice. Probably a couple of pleco species that would work here but would depend on how much you want to pay.
I've just shown these two channels in an other thread but worth having a look through because they are hugely knowledgable on central american cichlids. It would be worth looking at what they are keeping together and tracking how the tanks evolved and what was grown on for bigger tanks/ponds vs living life in a 180.
Lee Nutall -
https://www.youtube.com/user/lee1973n
Jim Cummings -
https://www.youtube.com/channel/UCXKTV3u2o44r5oGWQBdFe0Q
Big cichlids are always a risk, they are very territorial fish that in the wild would be part of a much greater hierachy or have acres to swim through so you have to be careful when combining them in a tank. But there are a lot of examples of successful cichlid tanks out there that we can use as examples of what can be achieved and how.
Wills