I was simply assuming that there's a "standard" length. Manufacturers have a tendency of "falling in line". It's good to know that 114 will work though, since that's how many you get with a SRAM chain, which is the only brand I buy any more (Yey, Powerlink).

I went ahead and ordered the Dahon Neos derailleur, even though it's $27 instead of the listed $20, on back order, and cost $10 to ship. I'll report back once I have it mounted. From pictures, it looks like I should remove the existing hanger, and mount it directly to the hole in the drop out for proper installation. I don't like that idea though.