I went to the Dunlop site and couldn't find the info I referenced above. It looks like they redesigned the site. Anyway I thought I better find something to support the statement above so here's a link.
http://www.partsmag.com/spring issue 993 (off road)/dunlop_editorial.html
About halfway down where they talk about the 739 they hint that it was designed in 98 to replace the K490 and K695. Some people still prefer the K490. Here's an excerpt:
Brian Fleck, Dunlop's Motorsport Off-Road Racing Manager in charge of product development, reported that the California tracks were perfect for the D739. "The track conditions at Anaheim and San Diego were pea-size rocks on top of a hard pack base," said Fleck. "These are the conditions in the past that Dunlop riders would have chosen K490 front and K695 rear. The D739s have changed that."