This is my setup for photographing books:
.. but I have issues with glossy books and magazines. I need help understanding the best place to position the lights so it covers the entire cradle (120 degrees) and produces even lighting.
Things to try:
You don't need anything fancy like polarizers to light your scene. To avoid glare you just need to place the lights so that there is no direct path from lightsource to camera by bouncing directly off your subject (i.e. the way a ball would bounce off). By lighting from a low angle glare will bounce off at a low angle and miss the camera.
For simplicity I've removed the second camera, but the same logic applies:
Placing lights in the green zones will guarantee no glare. If you move your camera back and use a longer lens that will give you a greater area in which you can place the lights without getting glare.
For evenness of lighting you'll want a symmetrical setup, i.e. one light either side. The further away the lights, the more even they will be also, as the distance from the lightsource to each part of the surface will vary less.