I'm not sure if the CR-78 ROM contains a basic Operating System for the D8048C or the data for the preset sounds accessed by the front panel buttons. Either way, I have uploaded the file.

The best option in terms of simplicity is to burn it to a 2732 Eprom, then bend legs 19 and 21 up and out of the way. Then, run a wire from pin 21, to pin 19, to pin 12 which is GND, so they are all connected up together. This will go in the socket the same way as the original 2708.