sweet, but what makes you think this stem now, is a one-off? The welds look cleaner on your old One-off, and the shape/clamps are all different.
I'm probably wrong, but I'm going with a Syncros/Titec proto or something to that effect. There's nothing else on your new ti fat that would suggest he was up on that high end, low production, handmade stuff from back then. Then again, it could've came on the bike. He added the generic cable stop, hmmmm.