Why not try it??
Some thoughts:
Make sure you have a least a 30 (front chainring) and 27 rear cassette for the climbs. If you run a compact crank (50/34) you need at least a 12/27 on the rear. Hills that you can climb easily are a LOT harder after 70-100 miles. These dang mountain rides I've been doing lately seem to end with the hardest climb the last 2 miles......and finish on top of a mountain.
Get in lots of climbing in the next 6 weeks. It's a real mental game to do 11,000 feet in 100+ miles. You need to know what it feels like to go 5-6 mph with no relief from pedaling for an hour at a time. It's a different set of leg muscles that you need to build up as well. You'll feel muscles just behind the top of the knee and your hamstrings get a good workout. Actually every leg muscle you have will get a workout.
Try and do sections of the route ahead of time just so you'll know what you're in for. The climbs after 50-70 miles will be a good bit harder on used legs, though. Some of that is helped with riding with others. Try and do the hardest climb before the ride, especially.
Eat before you're hungry and drink before you're thirsty.
Ride within your limits but you'll probably want to come up with ways to talk yourself into continuing to ride during the ride..........stay mentally tough. As long as you're going forward you're doing okay.
The finish is an incredible reward and quite an accomplishment.
And yeah......we're all nuts.