@XMIT: That's quite a project that you have put in front of you. Thus far, I've been satisfied with a relatively limited refurbishing of my Omnikey 101 boards. These are my favorite Northgates, because I don't have to mod the Enter key and I prefer not to have the extra width of the Ultra boards.
For all of them, this has consisted of washing the case and caps along with cleaning the top plate. For some, I have also sonicated and lubed the switches, replaced the alphas with PBT, and replaced the mods and spacebars with blank black ABS from Matias.
I usually also lube all the stabilizers, put some new 0.15 mm polyurethane foam under the spacebar inserts, and replace the spacebar slider with one from a Matias Quiet switch.
For some, I have also painted the top case. The bottom case usually requires only some cleaning, including sonicating the rubber flip feet. No more painting for a while -- it will be too cold in my neck of the woods until spring/summer. I am still in the process of evaluating different types of paints, including Duplicolor Vinyl & Fabric, Krylon, SEM, and VHT.
Finally, I install an internal Orihalcon-Soarer converter along with a panel-mount micro-USB connector. The connectors with extension cables from DataPro line up exactly with the holes for the PS/2 connector, so it is not necessary to drill new holes. I add a piece of "art foam" cut to fit the bottom of the metal pan, but I have not yet assessed what difference, if any, this makes in the sound of the board.
This overall treatment usually suffices to produce a good-looking and functional board. However, some of the top plates have a bit more corrosion than I would like. It is not really visible with the caps on, but knowing it is there gnaws on my conscience.
