>>1680482you would definitely need a new longer chain (good to change anyway for teeth wear reasons). You might also look at the 13-29 veloce 10spd cassette, which is a lot cheaper, if you don't mind giving up 1 gear at the top end.
Whether the derailer would wrap it or not depends on the cage length. There are short, medium and long cage derailers. Short, no, medium, probably, long, yes. Post a pic or try read model details off it. The info campy will give for the max cog is probably quite conservative.
The other thing you could do, is get a crank with smaller chainrings. You likely have a std 53/39 or something like that, and a compact (50/34) or even a subcompact (46-30) would also make a big difference. There are some compatibility issues for this too, but it should be doable, and the crank does not have to be campagnolo.
I lived in a mountain range for a while and regret not getting MUCH lower gearing on my road bike during that time. You really can't go too low. I think this pursuit on your bike is a very good one.
