You may or may not remember, but a few years ago I rescued a common and Gibby, both in terrible condition. They had lived together in a 3ft tank for 10 years. I eventually had them both in a rio 400, they got on brilliantly for a couple of years until Jethro (the common) grew larger than Gibbs. One day I heard an awful splashing in the front room. I found Jethro swimming round after Gibbs and side swiping him, it was relentless, poor Gibbs was on his side at one point, Jethro having managed to turn him over and was trying to swipe his pectoral fin into Gibb's belly. I had no choice but to separate them, it was one of the worse fish fights I had ever seen.
So yes they can live together, but there is a chance they may fight - bare in mind though mine did not fall out until Jethro was 18"+ and Gibbs was about 16" at the time.