Not familiar with this mill. A naive guess is that there could be an indexing/locking pin to make it easier to set the head at specific angles. But it would seem silly limiting its free rotation otherwise.
Considering that, so far, your only expenses are the moving expenses and considering that you have a very nice and not too common piece of equipment, unless you find a manual for cheaper, I would think that spending $200 for the book is far cheaper than any damage you can do to the machine.
Paolo
I'm trying to figure out if the vertical head attachment will pivot. It looks like it could but is either locked up or won't all together. I've put some leverage on it with no luck and just don't want to force it. I did pull the head and internally it looks like it might be 2 rings that sandwich a 3rd rig milled into the head to allow it to be loosened and pivoted. I hit it with some pb blaster to let it soak in so I can try to break it again later on, short of spending 200 bucks on a manual for it, I can't find any reference on if it will rotate or not, the few pics I found show it in the 90 degree config. I did see one pic with a slotting head attachment but it was 90 out and could have been clocked that way. Other than that this thing is a beast, it was a free bee just had to move it, that was fun rented a trailer, bought a winch, made a sled to drag it around and some 3/4inch drill rod to skate it around.