If you own a genuine Primal Rage PCB, you can flash the program and MO roms to update it to the final version of the game that only released in Japan.

Changes in this version include some alterations to a few AIs (mostly Sauron and Chaos), and separating out the Start button from the other four attacks; but the biggest changes go to special and finishing move inputs.

Specials that previously needed three buttons have come down to just one; inputs that required the Up direction have also been changed, and the 'Eat a Human' move that was unique is now a universal input. What all this means is the game can be played conventionally as opposed to the negative edge specials that it's known for.

You can try it out in MAME under primrage.zip, and if you want to do it for real, you'll need an EPROM programmer, an eraser (in case something screws up), some spare chips by Texas Instruments, and a pc.