Depending on how much the extension costs for the tank, I think my Dad would still do that. I think it will be cheaper than the overflows, considering the cheap ones are $80 a piece, and I would need a few.For all intensive purposes, your setup is pretty much identical to the gallons in mine so I would recommend the same pumps I'm going with: two Rio 20HF submersible pumps. Or, since you already have the Little Giant pump, and it looks to be rated about the same as the Rio model I mentioned, just use it and one Rio 20HF pump combined. I think it's a good idea to use two pumps so that you have a redundancy in case one fails, you will still have half of your flow until you get the other repaired/replaced.
The worst part about this is he acts like he knows more about the fish than I do. The only experience he's had with fish is killing my Grandmother's fish by turning up the heater to max when he was a kid.