What am I missing? Is this a worse idea than slugging it out with a tri-style bike that I already know fits?
Wow, this is weird. Did I get this right? You're riding a tri-bike on Brevets?
Yeah, you still don't get it. Don't take any measurements from that bike.
Go get some old lugged steel frame, put some bullet-proof wheels on it and ride. And don't get all stupid with the bags. Use the rear-rack and a trunk rack bag, never put crap, except your lights, computer on your handle bars.....
If you have to guess about the stem, go short, be ready to play with the saddle adjustment a couple of times on the 600k.