I suppose you've seen Buronson's new series that looks like it's a prequel to Hokuto no Ken http://www.haratetsuo.com/ looks like they even have a new Hokuto no Ken series or OVA movie? http://www.coamix.co.jp/ova/ apparently they are currently in production with no info yet..... :O
Yes, New Hokuto no Ken is OVA. This story is a subsequent events of ANIME.
Kenshirou's voice is Koyasu and new character Seiji's voice is Gackt!
The first volume is on sale 24.July in Japan. 6,800 yen. 60 minutes.