No one seems to have a sure answer on the diodes, this question seems to come up every six months. Some games have them on the schematics, some don't. Some put them on some coils but not others. It might help protect the bridge rectifier, but the bride *is* some diodes so...
Three options:
- leave it as is
- make it match the schematic
- look up the schematics for the last ems bally made any make it match *that* schematic, since maybe they learned a thing or two through the years
Either way, the potential issues that having or not having them can cause are minor, I wouldn't worry about it too much