The Unisystem VS has 2 8K roms available for the PPU. The CPU pin #37 controls which ROM is usable. Still not wanting to use two sockets and about 32 wires, I decided to use a single 16K eprom. Since I only have one eprom, I connected CPU pin #37 to A13. The /CE signal is connected to the PPU A13 signal directly.
I soldered the ROM on top of the PPU memory. Again, I used a small diagram to
compare the ROM and memory pinouts.