The EPROM mod is based in the work of Thierry Eppherre (he shared here in the group the hardware mod and a software to compile your own samples in a bank that the 707 can read).

The main difference is that I used a 27C4001 EPROM instead the of the 27C512 he used, and wired the 3 extra adress pins to 3 switches to select wich portion (bank) of the EPROM the 707  will see.

I did a small daughter board in a little piece of perfboard to reeplace the original EPROMs.

I attached some pictures.

Cheers.

Sebo