Tried it with oscars before, didn't work. Clowns ended up suffering, plus was unable to set up the tank specifically to cater for their needs as well as the oscars. Needless to say, the oscars went, they wern't a mating pair, but they did do quite a lot of damage, even with such a large tank (6x2x2).
Also have tried it with a green terror (quite mild temperment for a GT as well) couple of years back, again aggression was displayed towards the clowns, even though they were in such a large group.... the GT went.
Not to sure if it would work out, might be an idea to have a back-up tank, just incase
Ashleigh