Capacitive Discharge Ignition i.e.- MSD 6 or 7 series, Crane, Mallory, Summit, etc. Reason being that those boxes have a separate tach output and the tach should not be run off the coil as a conventional setup.I'm going to be honest and say that I do not know what a CDI box is...
Again, would someone measure their working filter, so we can find replacement parts?