Thanks for the sketch--it was a great help, as now I see how the rivers should work.
Now, regarding my mountains, I do have a question: would such placement be unfeasible? I really want to have a nice diversity of terrains in my map (including desert, that's why I've enclosed it on a mountain/hill circle, as that was the only way I've found to really have it on the map). The large chain you've sketched seems natural (a lot more than my 'popped mountains'), but I don't see it as an evironmental challenge to be explored. The main utility of this map should be as a setting to wilderness exploration, and I'd be willing to sacrifice some (not all) of the real placement in order to see an interesting place to be explored.