Did it in 2016 during my build-up to IM Canada, which was a mistake for reasons not really pertinent to your post. Although obviously extremely difficult, it's a fantastic event – very well run, great scenery, and great roads. How you prepare depends somewhat on your goal for the event. The common denominator is going to be doing as much mileage as you reasonably can do, with a consistent weekly long ride in 4-6 hr range (the event will take you longer, but a 7-8 hr ride is overkill, except maybe once or twice).
If you're looking to stay with a group or ride the climbs/KOMs hard, then you need to be able to do repeated 5-15 min efforts at FTP to VO2 max intensities and do them in the course of a 7 to 9 hr ride. For basically the entire course, you're either hammering up a climb at some insane grade, or descending the mountain you just climbed. So this means both dedicated interval sessions at durations and intensities that match what you plan to do on the climbs, and then later incorporating these sessions into your long rides. I wouldn't worry too much about not being able to simulate the terrain with your outdoor riding. Unless you live in Garrett County, MD, you're going to have a hard time matching the terrain anyway. Most of the climbs aren't very long, but they are all very steep and they come at you relentlessly. I don't think there are too many places like it.
On gearing, your 34x28 is adequate but maybe not ideal. I got by with a 36x28, but if I did it again I would want a 30 or 32. My friend who is super-strong (50-54 National Road Race Champ) did it with a 34x32, I think.
Good luck!
If you're looking to stay with a group or ride the climbs/KOMs hard, then you need to be able to do repeated 5-15 min efforts at FTP to VO2 max intensities and do them in the course of a 7 to 9 hr ride. For basically the entire course, you're either hammering up a climb at some insane grade, or descending the mountain you just climbed. So this means both dedicated interval sessions at durations and intensities that match what you plan to do on the climbs, and then later incorporating these sessions into your long rides. I wouldn't worry too much about not being able to simulate the terrain with your outdoor riding. Unless you live in Garrett County, MD, you're going to have a hard time matching the terrain anyway. Most of the climbs aren't very long, but they are all very steep and they come at you relentlessly. I don't think there are too many places like it.
On gearing, your 34x28 is adequate but maybe not ideal. I got by with a 36x28, but if I did it again I would want a 30 or 32. My friend who is super-strong (50-54 National Road Race Champ) did it with a 34x32, I think.
Good luck!