EXTREME Overclocking has just posted an article on Building a Stratum-1 GPS Based NTP Server with a Soekris net4501.

Typical GPS based NTP server appliances sell for hundreds, even thousands of dollars. Most have lots of features that justify that cost, such as an ovenized crystal oscillator (or even a rubidium standard), additional frequency outputs, custom web interface, commercial support, etc. Building your own basic NTP server (like in this article) can be done on the cheap for well under $200, and for all practical purposes gives just as good time over a network.

Building a Stratum-1 GPS Based NTP Server with a Soekris net4501 Article