Zombie vs Ninja / Gravedigger / Zombie Rivals
Right I've been trying to the bottom of this mess and have now skimmed through the "Gravedigger" and "Zombie Rivals" DVDs (they were dirt cheap at the time) flipping between the two to compare and contrast the differences (although I've not done a complete side-by-side comparison to check for minor differences in the scenes - it really isn't worth the effort ;) ).
So it appears we have three versions of the film.
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The Undertaker in Sohwa Province
A South Korean film that is the original source of this film.
http://hkmdb.com/db/movies/view.mhtml?id=10920&display_set=eng
http://www.hkcinemagic.com/en/movie.asp?id=9981
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Zombie vs Ninja
http://www.hkcinemagic.com/en/movie.asp?id=7256
This is a Godfrey Ho film that takes "The Undertaker in Sohwa Province" and adds in new material showing a bunch of western ninjas, in typical Godfrey Ho style (read his Wikipedia article for more background if you need it).
http://en.wikipedia.org/wiki/Godfrey_Ho
This seems only to be available in a UK DVD through Vengeance Video - the box says "Zombie Rivals," the disc says "Zombie Rivals: The Super Ninja Master," but the titles on the DVD menu call it "Zombie Rivals - The Super Master" and the actual titles on the film say "Zodiac America: The Super Master," which is a pretty impressive mess of names. This runs for 1:30:42. It also includes a "coming soon" gallery of stills and the trailer that can be seen here:
http://www.youtube.com/watch?v=XcT-9rizfa0
DVD (which used to only go for a couple of pounds but no appears sold out):
http://www.amazon.co.uk/Zombie-Rivals-DVD/dp/B0007V5X86/
VHS (check out that box cover!!):
http://www.amazon.co.uk/ZOMBIE-RIVAL-SUPER-NINJA-MASTER/dp/B0056S06MS/
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Gravedigger
This is a reworking of "Zombie vs Ninja" in what appears to be an attempt to reconstruct "The Undertaker in Sohwa Province", which confusingly leaves in the "ZvN" dubbing (and most of the titles, just snipping off the very start with the previous name, "Zodiac America: The Super Master" - they do try and correct the credits on the box: "staring Elton Chong, Larry Kim, directed by Elton Chong" even though the HKMDB gives the directing credit to Kim Jung-Yong), even though they have stripped out all the added material.=
It has been released as Gravedigger by the Wu-tang Clan through the Soul Assassins label at Ground Zero (who also seem to have released it under their Black Belt Theater line of cheap, low quality kung-fu films - although checking the publisher is given as "Genius Products" or "Genius Products/Vivendi Visual") and it runs to 1:15:02. As I don't know the run time of "The Undertaker in Sohwa Province" it is difficult to say how successful this reconstruction has been but there do seem to be bits missing that were used to merge the new footage in by Ho. It seems a pretty crude and cheap, hack and slash that ends up with less of the original film, so I can't really see the point in this - release "TUiSP" from an original print or don't bother at all.
http://www.amazon.com/Gravedigger-Elton-Chong/dp/B0000D0YVY/
http://www.amazon.co.uk/Gravedigger-DVD-Region-Import-NTSC/dp/B0000D0Y VY/
http://www.amazon.co.uk/Black-Belt-Theatre-GraveDigger-REGION/dp/63094 23479/
http://www.amazon.co.uk/Black-Belt-Theatre-GraveDigger-Region/dp/B0009 PW4GO/
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Further confusion could sneak in as HK Cinemagic lists "Gravedigger" as the name for the Honk Kong release of the "The Undertaker in Sohwa Province". It might be the Ground Zero release deliberately used this title to reflect its attempts to get back to the original film, but what they've released isn't the original
http://www.hkcinemagic.com/en/movie.asp?id=9981
Also HKMDB says that "Zombie Rivals" was also an alernative name for "TUiSP":
http://hkmdb.com/db/movies/view.mhtml?id=10920&display_set=eng