NeoBiosMasta
The NeoBiosMasta mod boards were designed by User:NeoTurfMasta to simplify the replacement of the original system ROM by alternative ones such as the Universe BIOS, on systems which were known to be troublesome.
Early MVS PCBs and the front-loading version of the NeoGeo CD had their system ROM in a DIP package, which made replacement relatively easy. Later PCBs used surface-mount ROMs which required desoldering and adaptation of the footprint with about 40 wires.
These boards clip on the 68k with an upside-down PLCC socket to tap the address and data bus, and require only 2 wires to catch the decoded /OE and /CE signals.
MVS version
Available for purchase here (+ installation manual): http://neogeofanclub.com/project/neobiosmasta/
The PCB design is freely available, and can be ordered from OSH Park: https://oshpark.com/shared_projects/FMUCIk4m