Hi, when it comes to larger fish its important to be accurate with your tank sizes, the width is obviously key as a narrow tank means a larger fish won't be able to physically turn around, If the tank is commercially known then this makes again makes things easier
Also when working roughly, 40" long can easily turn into 3' which would be too small for Severum,
For two gold severum I would be looking at a tank somewhere around 75-100G (280-380L) with a width of no less than 18", These are big bulky fish that should easily be 9-10"+ within the next year.