As far as I know, most people believe that the only way to be sure if you have a 1.00 version is to play to level 3 and see if the flamethrower guys have hair. Here's a way that I think works (Unless I'm proven wrong) to check without playing the game.
First of all if you don't know the differences.. *Stolen from Wiki*
Software revision 1.00 (1989): Enemy characters resembling Rambo, The Terminator, Spider-Man, Batman, and Godzilla are present. Both Spider-Man and Batman are actually fake representations of the characters conducted by a shapeshifter who alters his appearance after sustaining a certain amount of damage. Additionally, Joe Musashi's face on the title sequence resembled that of actor Sonny Chiba dressed as his character Hattori Hanzō from the Japanese TV series Kage no Gundan (Shadow Warriors).
Software revision 1.01 (1989): Batman is replaced by a winged Devilman-like creature. Godzilla and Spider-Man remain unmodified, the latter now morphs into the Devil when defeated. The "Gunner" enemy soldiers with flamethrowers are also changed to bald men with headbands, altering their original likeness to Rambo (although Sega had the license to the character for their Rambo III console games, they did not use it for this game).
Software revision 1.02 (1990): The fake Spider-Man is now redesigned into the licensed character from Marvel Comics, acknowledged by a copyright notice (Sega already had the license to the character for their game The Amazing Spider-Man vs. The Kingpin). Since he is now the real Spider-Man, he does not morph into the Devil and actually leaves the battle when enough damage is inflicted, with the winged Devil entering to replace him. Godzilla still remains intact.
Software revision 1.03 (1990): Godzilla is replaced by a skeletal dinosaur. Everything else remains intact from the previous revision, including the licensed use of Spider-Man. This version was used in the Genesis 6-Pak cartridge along with the "Sega Classics" edition of the game.
Software revision 1.04 (2009): Since the licensed use of the boss Spider-Man was for a limited period of time, the game was subsequently prevented from being re-released years later. The 2009 release for the Virtual Console features a new specific software revision (1.04) that omits the Marvel copyright notice and replaces Spider-Man with a pink palette swap of the character that still behaves the same as the licensed Spider-Man.[4] Joe Musashi's design in the title screen was also altered to remove his likeness to Sonny Chiba.
In a nutshell, 1.00 is the version most people want, as it has all of the unlicensed super heros in it.
I've got all versions now, so hopefully this will help anyone looking to get a 1.00.
First check the back, if it looks like this, it might be a 1.00, but it also may be 1.01
If it looks like this, it's a Sega classics version and is 1.02
On my 1.00 cart the words Sega are on the top of the chip.
On my 1.01 the words Sega are now "Sega Japan" and are in the center of the chip.
On my 1.02 cart (Although you shouldn't need to open it anyway) looks like this. Very Different.
( The resistors has been proven to not be relevant, as seen in a post below there is a 1.01 cart with the small one.)
Hopefully this can help anyone looking to get a 1.00 cart!