I made a couple of JAMMA fingerboards to complete the JAMMA conversion set, to allow for the creations of custom JAMMA harnesses or extensions.
These come in two flavors, narrow and wide. Narrow is approximately an inch wide. It can be used where space is at a premium.
Narrow size 
Clear JAMMA labels
The wide version is approximately 2 inches wide, and gives better leverage when plugging in unplugging your harness. The additional surface area also provides better wire stability.