What does netdate want back from udp-37 server?

[simonst@WellsFargo.COM]

I'm trying to write a mainframe (MVS) timserver (udp-37 only).  I test it
with a Debian 2.0 cmd "netdate udp <mvs.ip.address>", which sends a 1-byte
0x0A message.  My server sends back a 32-bit unsigned number (# of seconds
since 1900-01-01, per RFC868), but the Debian netdate command times out.

 1. Why doesn't the netdate command send an empty datagram, per RFC868?
 2. What exactly is netdate expecting back from udp port-37?
 3. Why does RFC868 mention negative 32-bit values: -1,297,728,000 "17 Nov
1858 GMT"?

I would appreciate any help (or where I might find the netdate source).