The Ronstan 19mm ball track ( like on 29ers ) is good, but you must get the undrilled track it you want to bend it. It only needs support at the ends and middle if it's prebent. The 49er track is a bit sturdier, fits Ok and works as Will said.
The 29er track is predrilled, but not bent, so this is only Ok if you bend it into place and use hundreds of bolts on a curved bit of structure.