assume you are talking transalp race??
I did it in 2003 on a 26" used maxxis Larsen TTs.
on a 29er i would go for the fastest rolling thing you can get , but one with a bit of sidewall knob for the front.
most of the downhills are dirt road with good clean lines but with some fast corners, so you want the knobs out wide for this.
I would run something like a gearx barro onthe front and small block eight on the rear, or if you want big volume a racing ralphs.