Originally Posted by desertdork

Your current setup (with triple crankset) must have a long cage derailleur. But it's a road long cage der ("GS" in Shimano); this is different than a long cage "mtb" derailleur ("SGS"). The GS lacks the chainwrap and higher maximum cog capacities of the SGS. Deore and Deore LX SGS derailleurs can be bought for <$50.

And you can indeed run your narrow range cassette with the longer cage; there aren't limits at the other end of the spectrum, only a slight penalty in weight and (possibly) shifting speed, but those aren't concerns when touring.