I have seen and I am an inveterate used book buyer!
Mastering Weave Structures by Sharon Alderman.
It is an expensive book, so not to be invested in if you are not hopelessly passionate about weaving. If you are it will not only educate you extremely well, but it will also explode your mind.
Detailed article on replacing nasty string heddles with texsolv on a direct tie-up, 4-shaft Ullman loom. It's a bit of a tricky chore, but done carefully, and slowly it goes smoothly. Goes much better with a helper. The instructions are in a pdf file, because that's quicker than making a web page and I want to spend time weaving, not coding!
When I got my Ullman, it was folded flat and I'd never seen a loom of any kind before. So of course I looked for help on the web. Nothing. I struggled and looked at pictures of other jack looms and managed to get it up and functioning. I am puting this page up with images that might help others. There are a number of these Ullmans around and they are great beginning looms. Sturdy and well built.
For Beginners Like Me: Just some basic info on sett in tapestry and what gets rid of lice (bits of warp that show on the tapestry face).