I presume it would be possible to use a CPC+ CM14 monitor with an original machine with the appropriate DIN adapter and voltage converter to get 12v for the drives?
But CPC 464+ and 6128+ use only 5V line.
You need only an adapter for the correct RGB signals and the 5V.
It is possible, yes. You need a specific cable for the video connection (in E-bay they are sold to allow you to connect a Plus to a normal screen, but you can always ask the seller to do the opposite or make the cable yourself) and then sort out the problem of the 12V for the disc drive. A 5VCPC (the board from Bryce) could be a great option for this. Otherwise, an external power source should to the trick, but do not connect two power supplies to the same machine. Using the 5V rail from the screen and an external 12V PSU for the drive is not a good idea.
Just for you to see, this is a normal CPC 6128 board that I am modding connected to my CM14 :) The power for the computer comes from an external PSU, though, I am not using the 5V from the screen.
(http://www.cpcwiki.eu/forum/index.php?action=dlattach;topic=13116.0;attach=22310;image)