Depending on routes taken, some pass roads have a very short length limit. Some limit to 35 feet (Independence Pass). The I.P. going down into Aspen from Leadville (dont drink the water) is a single lane wide at points with no traffic controlling devices. So be wise with your route.
Remove the broncos driveshafts to flat tow. It is safest.
Use your transmission to control your decent and use the brakes only when needed. I've towed my bronco on a 2200 pound trailer with my 2008 5.4L F350 but it has 4.10s and a six speed manual trans. Just take it slow and realize you arent gonna be going like a commuter car. Stay in the right lane and let all the yayhoos fly by you on the left. The 5.4L 3v engines LOVE 3500 to 4500 rpms. Let it EAT! It makes it most power in that range and you'll need all the power you can get.
As for the 89 above the treeline... You wont have much power. It will run fine, there just isnt the oxygen available to make probably 60% of normal power. So use a lower gear than you might normally. Driving that high affects every vehicle, not just carbs. High altitudes are also very taxing on the cooling system so make sure its up to snuff and you have stuff to fix it. And fill it... Last but certainly not least is having good brakes. You dont want to pull a Thelma and Louise!
Enjoy yourself! Southern and Central Colorado is a beautiful place. If you make it to Creede, eat at Kip's and tour the fire station (inside a cave!)
