No way would I go with that much room. Is the 29 gallons before evaporation? Probably boil a couple gallons off, but to start with, that's way too close for me. 20 gallons in my 25 gallon kettle is really cutting it close.
Too tight, we use a 20g kettle and a 15.5g keggle to boil 30 gallons and it gets close at hop additions. It could be done if you really watch your burner and are standing by with a hose. Definitly a 2 man job and wont be easy.
That's not to say that it can't be done. You can always add more wort halfway through the boil to top it off, but as far as a consistently easy boil, that's just too close for me personally.