I can't really say for sure since I haven't played it, but since it's a Working Designs release, there might be instances where the company changed stats/things around in the game. It might be worth checking in on that one guy who is hacking WD releases to remove their stat-change f*ckery to see if there are any major gameplay differences between Vasteel's JPN and USA releases.
If anything, my money is on the Japanese release being better balanced, being the original and all. No guarantees though. :-"