So I've verified that the project works with the code provided.  So now we have a proof of concept to move a file from one SD card to another one-way through an opto-coupler.

To prevent corrupting the file a bit (not sure why that's happening), you have to plug in the transmitter first, then plug in the receiver, then hit the reset button on the transmitter.  By plugged in, being plugged into a USB power source is sufficient.  After the reboot a clean transfer will happen.

I found it odd that just using one wire to transfer, some corruption wasn't happening, but adding my opto-coupler board (labled "Tinfoil Transfer"), there's some weird data being sent to the file.