That should do ok for a asian arowana, the three foot width on the tank is much more suitable then a two foot wide tank, I consider a two foot wide tank to small to house an arowana.
the asian aro's i've seen, they rarely exceed 2 1/2 feet unless you put them in a huge grow out pond then transfer to the tank. silver's do get bigger though... I have heard of 19 yr old australian aro nearing 3 feet