Only the DJ70 mkII have a SCSI interface. Roland does not offer a upgrade for the DJ70.
An old document from Roland site (dated 1997) provides a company in Italy that does SCSI modifications, but maybe this information is outdated.

Look for the DJ70 supplemental notes at: http://www.rolandus.com/SUPPORT/DOCS/SUPNOTES/DJMKII.HTM
The same document also in Adobe Acrobat format: http://www.rolandus.com/SUPPORT/DOCS/SUPNOTES/DJ70SN.PDF

Mgomes