I managed to get this machine ultra cheap as the business selling it was going broke.
Sun's Netra T1 range of servers are the Telco grade version of the X1.
The T1 105 I have is the 360mhz UltraSPARC-IIi @ 64bit. Has 512mb of memory via two of the Mezzanine cards.
The T1 used Mezzanine cards that you could stack together to get more memory they do not have traditional memory slots. Maxium memory is 1gb The T1 supports up to 2x 80pin SCSI drives and an internal CD/DVD-rom drive using suns weird CD-rom paddle board. You can easey make this as the IDE header on the motherboard is a standard 44pin IDE interface. It can also support HDD's or CD/DVD rom drives.
You can find some work I've done on the IDE connector and fan mods :