you could probably have bichirs in there will a solo fish but as soon as fish breed things change and some pairs decide nothing else will live in that tank and a bichir will not stand a chance if that happens. if you want the bichirs id stay away from getting a pair cause you will most likely end up with only the pair in the tank especially if you get a 75 which is bare min for a pair imo
my uncle has a cross bred african cichlid, the male is the only one left in the tank, because once the tank was filled with african cichlids and 2 plecos, the male and a female mated and they had fries, so the male killed every cichlid in the tank except the mom, he also ate the 2 plecos, later on the fries were part grown and the male suddenly killed all the fries and he killed the mom so he is alone forever