Mokelembembe are actually one of the smallest polypterus species and depending on the dimensions of the 60 could stay in there for life. I would suggest sand substrate (black specifically), because it usually enhances their colors if you use the right substrate and they can easily choke and die if they accidentally eat gravel if they are on gravel substrate. Their food would be mainly bloodworms, brineshrimp, pellets, when they were small and when they grow larger they can still be fed those and also you can add tilapia, silversides, catfish, and many more things. The temp they usually like around high 70's and low 80's. Actually you might be better off keeping it in the 60 for a while, because since some mokes have very shy personalities they may not eat for a while and in a large 200g-300g tank they could easily miss out on eating if the tank mates get to the food quicker than the moke.