Depends some 1200gph have dual hoses so you could always close one off if you are skimming to much water.
But yes if your tanke is not drilled get an overflow box but don't buy a cheap one, I bought one and it was crappy. The plastic screws broke that held the damn box in the water to adjust how much it takes in.
I love my CPR overflow box. on my 75 gallon. But you may have trouble fitting a 29 gallon under your stand. I have a 29 gallon under mine and I actually had to put it in from the top because it would not fit in from the back or front.