The GOG version appears to be the TurboGrafx-16 rom and Mednafen emulator. The source code for the emulator is included in Impossamole\src.zip. Also Impossamole\Res\game is a rom file. Just rename it Impossamole.pce and use it with the emulator of your choice. Personally I found MagicEngine to run smoother. Mednafen let me use the start button on an XBox360 pad but the action buttons are reversed compared to a TurboGrafx.

Have fun. It's Impossamole!