I made one of the monochrome cables for my 128 before I got my 1902 monitor, and it works fine. I used it with CPM, and didn't have any problems. I am not sure what monitors will work with the 128, as it has the digital RGB output, but I know the 1902 does, as that is what I use. I also have made one of the S-video cables for mine and have it hooked to a small LCD TV for 40 column use. It works fine as well. I know this isn't much help, but just thought I would add my experiences to the mix. If I can help with testing or anything, let me know.
Jeff