Seems like youd be better off sticking with active fish in one tank, non actives/slow fish in another. Balas, Oscars, etc are active, will most likely out compete the needle nose 'gar' for food.
Maybe try putting a couple 'gars' along with a couple other ancient fish in another 150g.. some slow moving fish that will have an equal chance/opportunity to get fed.. i was thinking of adding some Balas to my 70g with my juvenile Delhezi, but seeing as theyre technically blind, i'd be better off to add other bichirs or a couple ropes... something with a simular activity level/eating habit...