If all SixOThree has is a Coco, the only practical method for moving the cart ROM to a PC for posting on the Web is by creating a .wav file. As robcfg indicated, the cart must be taped to prevent an auto-start.
Cart auto-start happens when a signal goes from edge connector 7 to edge connector 8. All the odd edge connectors are on one side of the board with even on the other. Connector 9 is a short trace, easily spotted and identifies the odd side. Put tape over edge connector 8.
Now that the cart will not auto-start, the Coco can send an audio sequence to the PC to be saved as a .wav file. This is done with a modified cable normally used to connect the Coco to a tape recorder. Coco cassette out pin 5 is signal and pin 2 is ground.
A simple Basic program can be used to send the audio signal to the PC.
The above lines will copy all the data in the cart ROM. The .wav file can be loaded into appropriate emulation software and saved in proper binary format for use as a .rom or .ccc file for use with MESS and other emulators.
One final point, the above will work with a Coco1 or Coco2. A Coco3 must be put into RAM/ROM mode or the cart can't be accessed. POKE&HFFDE,0