Grumdril
Vassal
Sorry Harry. My lads thought the unicorn would be tasty eating once properly tenderised 
Re. the arc restrictions, I'm not sure that's really necessary, but YMMV. My reasoning being that if you're deploying "by the book" hence slowest units first then the placement of the war machines will be first (except for dwarves on account of their stunty legs) and hence something that the opponent will be able to react to accordingly in their deployment. So the war machines and their clear field of fire is quite a major decision and, due to their slow movement rate and the fact they can't move/turn and fire, one that their owner has to live with for the duration for the battle. Which it seems to me probably how things should be. The only issue in this event is if speculative fire is too accurate.
And if you're not going "by the book" then the chances are you've got some sort of scripted setup and probably even a GM, in which case this rules detail is probably less of an issue.

Re. the arc restrictions, I'm not sure that's really necessary, but YMMV. My reasoning being that if you're deploying "by the book" hence slowest units first then the placement of the war machines will be first (except for dwarves on account of their stunty legs) and hence something that the opponent will be able to react to accordingly in their deployment. So the war machines and their clear field of fire is quite a major decision and, due to their slow movement rate and the fact they can't move/turn and fire, one that their owner has to live with for the duration for the battle. Which it seems to me probably how things should be. The only issue in this event is if speculative fire is too accurate.
And if you're not going "by the book" then the chances are you've got some sort of scripted setup and probably even a GM, in which case this rules detail is probably less of an issue.