you will need to buy a SCSI controller card and some SCSI cables (im assumeing its a U320 SCSI drive. run its model number through google to confirm)
if you already had a SCSI controller card and cables i would have said as long as it cots les than $30 u didnt do to bad.
unfortunatly scsi cards dont come cheap. and even the mid to high range U320 SCSI cards will only perform about as well as a 1tb Black Edition Western Digital (SATA II or III).
these cards should work in ur 990X board.
i wouldnt bother with the HDD. a new 1tb WD Black or equilivent will be quicker and store more while still being ~$100