Yes, the reference photo I used was found while browsing Photobucket. In the photo they had halters on, though. I wasn't brave enough to try those. :)
If f I may put my oar in, I think it was a very good idea not to include the headstalls, as the horses look more relaxed that way. I wouldn't give up on tack altogether, though, (which I'm sure you haven't). I myself find it a pain and a half to draw, but I think it's well worth it, especially when working in color, when you get to make the shiny brass rings and buckles really show up, which gives the painting contrast and authenticity.