On the old Motorola CD ignition, black was a ground for the coil--if you put voltage into the positive terminal, it needs somewhere to go or the coil will act like a capacitor instead of generating a high voltage pulse. Thus, the short black wire grounds to the engine through the distributor mount. It really could be any length and ground anywhere on the block. If the new coil is grounded to the mount, (probably through one of the mounting screws) you probably still need the ground wire because the mount will be attached on the rubber isolators. If this is the case, ground through the mounting screw that is on the coil ground strap.
The white wire was always a tachometer signal wire while the red wire was a constant 12 volt power source to the Motorola capacitors, whether or not the ignition was on. Blue wire was a switched power source for the internal electronics in the Motorola AND the electric eye in the electronic distributor (if the engine had one
Don't know your replacement CD box but you can probably figure it from the above. I suspect that the internal capacitors are now switched along with the CD box main power source and the red wire is simply not needed.