I would recommend a small group. Someone always tends to have something you forgot. Safety can be an issue. Practice on hills an do some walking. We walked about 2/3rds of the way. If you ever go, I can help out by giving you what we used that worked.
This was not as physically hard as a 100 miler or a road 100K. I mean, it works you, but I would say if the distance is covered reasonably then it is similar to the demands of a 50 miler one would run fairly hard.
Since we were all experienced ultra runners, the time continuum and persistent grind was something we managed well. It appeared to us that many of the rim to rim crossers bit off more than they wanted to chew. Way over or way under packed or prepared. No real commitment to the group or contingency plan. When you run into people and they are maybe averaging 1 mph, facing darkness, are beat, loaded down, and still have at least 7 hours to go; one wonders how does anyone without ultra experience make it? No wonder there are like 300 rescues a year.
The hardest part is stepping over the logs and rocks in the last 5 mile stretch. Your laterals are shot. Have a plan, do some research, train accordingly, and ask the Rangers questions before you leave. Time of the year is important. They shut the water off in many areas after October 15th.