Part of this depends on what you want to shoot - landscape, birds, otters, big game like elk/bison/bears, wolves, etc. Yellowstone has all of that and more. It also depends on the time of year but I'm assuming you are going in the near future.
If you really want to get wolf shots you have to be incredibly patient and understand that they will be some distance away most of the time. You'd want to have the 7d + 600 + 1.4 to get any decent shots. They get closer in the winter incidentally and even then I was wishing I had more range with my 7d + 500 + 1.4.
Most of the other wildlife isn't too far away. Looking at my pictures from a summer and winter trip to Yellowstone before I was getting a wide variety of wildlife in focal lengths that were usually < 500 mm equivalent with few exceptions. Notably there will be great photo opportunities while driving or hiking that will require a wider angle lens and sometimes without warning so I'd drive around with two cameras ready to go - one for telephoto shots and one with something wider for scenery and the occasional animal close encounter.
Sometimes I'd see amazing shots of lumbering families of grizzlies roaming the treeline quite a distance away and would want the range but often the bears aren't incredibly far away or at least you are able to reposition to get a better shot while still at a safe distance.
My suggestion if you are looking to shoot the full variety of options (and Yellowstone really offers an amazing variety of photographic opportunities) is to bring the following:
Either 5d3 or 1dx - after buying a 1dx my heart would tell me to take it on this trip but my brain would say to take the 5d3 instead. I'd consider the 5d3 instead because of the additional resolution and the size advantage however it is arguable whether it truly matters. The increased frame rate of the 1dx won't be a major factor on this trip and the better low light capabilities of the 1dx would be somewhat handy but not critical.
The second body should be the 7d for the extra reach unless you have zero interest in wolves and birds and distant animals. You'd probably not be too bad using one of your FF's instead + the 600 + a tc but if you are looking at truly distant subjects (or smaller things) you will get more pixels on target with the 7d. So if you don't care about farther away stuff take the 5d3 and 1dx.
Your lens selections sound spot on.
I don't think a blind is going to be worth it. You can see amazing wildlife in Yellowstone through a combination of patience, getting up early, talking to locals and park rangers (like the various wolf experts - look for the yellow SUV), and considering doing at least some guided touring. There are an incredible variety of good guides around and actually the Yellowstone Association does some nice tours as well. My summer visit was without any assistance but my winter visit was with the YA guides as it is logistically complex to visit most of Yellowstone in winter.
It also doesn't take much hiking to get away from the masses and see good stuff. This is a nice contrast to Yosemite where it seemed like you really had to hike a bit to get some of the best experiences.