I know you can't run.
But you can do a running style training plan.
For runners- it's one speed type workout a week- which is short sprints OR reall hard for slightly longer distances OR tempo ride (for a 6 segment exercise- one segment for nominal warm up- 4 at a pretty high rate- faster than your long one- and one cool down). Oh, or hill repeats.
As you get better, you can do two of those a week.
But for now, I'd say once a week, and then start a 30 day challenge weight thing. On that, I do one 30 day challenge for my legs, one for my abs, and one for my arms. Start short, as they get super hard by day 30- but it helps a lot.
For the weekend- long rides at a rate where you can still talk. But almost with difficulty. This will be pretty close to you aerobic upper limit. You can use a HR monitor (which I do) to get it right on, if you'd like.
Inbetween all of that- shorter, slower recovery rides.
Since you want to do really long rides, find a couch to marathon plan- and adapt it to riding. Stick to it. They really work well.
The important thing is that you are doing two things with the plan- increasing your anaerobic ability through the stregth/speed work and increasing your aeroboic ability with the long events. The marathon plans are really interesting- you see most of the long runs are slower or much slower than marathon pace, so it's kind of confusing- but the end goal is that the aerobic + anaerobic workout timing match up with the event you plan to do. And it does work.
My personal favorite are the spints- not because I actually like them, but because I could see the results of those the following weekend- where I could run faster with the same HR effort as before. It's pretty amazing.
Hill workouts were interesting too- as I tried to pay attention to my recovery rate- so by the time the race came around- I had confidence that I could keep my pace going up a hill, as I would recover getting over it.
It's easy to overdo it- and hurt yourself. This should NOT be "no-pain, no-gain" thinking. It should be a long target.
Good luck! And enjoy the view.