A colony of tilapia will kill the lungfish regardless of the lungfish size especially nile tilapia. Tilapia loves to eat the lungfish skin. I had a group of nile tilapia and blue tilapia as feeders for my lungfish. Lungfish was a 36" congo marble lungfish. First 2 weeks was fine till the tilapias got comfortable and develop a taste for lungfish skin.Works great. As long as you don't care about the tankmates.
Try a colony of tilapia or convicts as self refilling feeders.