Arowana, Florida Gar and Clown Knife can all grow to 3'+. Depending on what type of PBs you get you could be looking at 3 fish that should grow 30"+.
One of the reasons you don't see too many of them on here that size is because people try to keep them in undersized tanks (i.e. 220G). A 300G would be way too small for all those monsters.
I would say you have at most 2 years in the 220G if you get them all at under 6 inches. Then an upgrade to 10x4 (600G) would be in order as a long term home.
There are plenty of fish you can keep in a 220G for life. Why not stock the tank with species you can keep in it for life?....just in case you don't land this dream job you refer to.
A Florida Gar will usually max out at 18-20".
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