That is way to much for a 55, the std rule of tumb is 1' of fish per 5 gal of water and it is measured at fully matured size for the fish you add. even though the lion is not a open water swimmer it needs a larger terriitory than what would be available in a 55, and 2
tomato clowns (which can get to 6" each) are very apt to fighting. By the time you add rock, substrate etc. you can reduce the actual amount of water to as low as 40-45 gal so you really should not have more than 8"-9" of combined fish length.