Have you looked at the african biotope thread in the photo lounge for ideas,the humpheads are you talking about steatocranus casuarius or we call it the blockhead?.
Weve got one which seemed to get on with our bichirs but only gets to around 6.5" which is what ours is,nice fish but is basically a bottom dweller.
You definitely DO NOT want to put a congo puffer in a community tank... since its will just be a matter of time before it tears all your other fish limb to limb.... not to mention they aren't very active and tend to stay buried most of the time waiting to ambush prey...