Looks like we have to have SSN (which they will allow you to give verbally, which seems odd), proof of address, and one of the following: passport, birth certificate, cert. of citizenship or naturalization or birth abroad. I guess they don't accept the newly-expiring DL anymore. Guess I'll be sending off to Santa Clara County, CA, for another copy of the birth certificate.
The nice thing I just noticed is that if you have a 15-year history of driving in MO, they'll give you what's basically a provisional license (can't be commercial) that's good for a year to allow you to get your documents together. That's cool of them.