Skaarg released a nice prototype of this game after buying it off of DreamTR's lot and was kind enough to provide it to everyone for free!

You can grab it here:

http://www.megaupload.com/?d=7GG06WJ4

There are noticable differences right off the bat, you can read up on some of them over at Retro (lol):

http://forums.sonicretro.org/index.php?showtopic=22330

Enjoy!