We've done this a few times on this site. Theres some good advice in these threads:

1 1/8" stems that don't suck..? (threadless)
http://www.bikeforums.net/showthread.php?t=103186

Track specific threadless stem?
http://www.bikeforums.net/showthread.php?t=91316


The Thompson stems are really nice, but 15 deg drop is really not going give you much of a slant and on most bikes its going to be close to neutral when installed. So if you want an old school slope to your stem you need to look elsewhere; otherwise its a great stem.