Thank you Matt and Prizrak, I wanted to post this yesterday but I haven't been getting much sleep these days.
My friend Curt found the cart back in 1997 at a flea market in NJ. He thinks someone may have cleaned out the Imagineering offices (which were an hour away from the market) and started selling off the stuff there. Last year he gave it to me for my show, and Rob (Ballblazer) dumped the rom for me in February. Dennis Debro disassembled the code and found a lot of the differences that happen later in the game, as did GlitchCat7, who previously held the Frostbite World record. I am very grateful to all of them. Hopefully Dennis doesn't mind, this is the list of differences he sent to me:
Looks to be no day and night scenes
The game ends after reaching over a million points. Score gets set to 999,999
The temperature value modulates colors instead of blinks when below 10 degrees
The number of lives doesn't "flash" when below 10 degrees
Magic Fish icon shows when player reaches level 24
Polar Grizzly appears after Level 2
Igloo door doesn't flash in DEMO mode
Only 2 game selections (i.e. ONE_PLAYER and TWO_PLAYERS)
There is no fish maximum per level...player can eat as many fish as produced
Production release no longer spawns fish for a level after the player captures 12
There are no Killer Clams
New obstacle (I don't know what that yellow thing is to be)
King Crab graphics are different
Fish colors are different
Additional Fish object (there are green fish and blue fish)
The game speeds look to be increased in this proto. I didn't get to deep in the math though.
Here's a picture of the cart, my phone is only letting me post one for some reason.
I've also attached the rom if you would like to try it out. (Edit: I missed the part where Prizrak posted the rom, sorry)
Iceman (Frostbite Beta) (07-27-83) (Activision, Steve Cartwright) (Prototype).bin