What I meant is that as long as the horse is healthy and sound, the conformation is usually going to take a back seat to everything else. Yes, conformational issues will affect the same things that it affects in any other type of riding. But if you're not having any problems with what you're already doing, you're likely going to be fine on the trail. On the other hand, the things Joe4d listed are very important and will make or break an endurance horse that would otherwise be perfectly fine doing other types of riding.
If I were looking to buy a horse, no matter what discipline, and buy the best horse I could possibly afford and like, including conformation. For endurance, I would look for an Arab or half Arab, since that gives you the best advantage for what you want to do. And that's exactly what I did do. However, there's no reason to feel like you can't do endurance with the horse you already have, assuming it's sound and healthy. Beyond that, you'll have to listen to what she tells you out on the trail to determine how great of an endurance hors she could be.