I'd do two oscars, some polys for the bottom (big clown loaches would be cool but hard to track down) and then something that sticks to higher level...although my senegal liked to sit in the floating fake plant. I am not familiar with gars, but I am to the point of seeing them in person and knowing they are very rigid and not flexible. As a whole, of the few oscars I have had, they are a peaceful fish so as long as something can't fit in their mouth, you are good. I don't know your filtration but you could probably throw more CA&SA cichlids in. I had a heavily overstocked 90 at one point (with an oscar, 2 jags, a flowerhorn, senegal, pleco, the pictus lookalike that gets larger cant remember name, a jewel cichlid, and I'm sure I am forgetting stuff but for the most part as long as the clay pot was in place they all got along). I also had a fx5 and AC110 on it.
