Go see a doctor (start with your GP and get referred to an orthopedist).
For the (postural?) kyphosis you need to strengthen your upper back.
To reduce the visbility of mild symmetric pigeon chest you need to build you chest muscles.
In order for muscle hypertrophy to occur you basically need to do anaerobic exercise BUT this could be VERY dangerous for you depending on the severity of your kyphosis. Find out what kind of lifting you can do with condition and do it. You might want to check out http://forum.bodybuilding.com/
Well sounds like a mixed martial art will do? What about Boxing ? (and you don't have to actually fight in competitions, the training should cover those aspects).
Is your fear of drowning limited to big open dams? Or don't you swim at all? Swimming should also do alot for your upper body....
Anyway, i also cycle and i run and between the two i always feel i get a more fully body workout when running, especially upper body (despite your legs doing the bulk of the work) . So if nothing helps, i'd at least try and go running...
My curvature is not severe or pronounced enough for people to recognise if I'm wearing a shirt, most of the time people don't notice even if I'm not wearing one. But X-Rays reveal all...
But the pain is horrific.
I suggest you do some swimming in a shallow pool, due to your fear of drowning. Perhaps go to a GP and ask for a benzodiazepine that may help you overcome your fear.