Originally Posted by kroozer

Henry III is/was making long cages specifically to fit a Campagnolo NR/SR rear derailleur. That would allow you to use an even bigger freewheel like 32 or 34 teeth. Look for his recent post in the For Sale thread.
But first try a 28t FW, it will make a huge difference from a 23t, maybe enough. 42-23 is insane for the mountains.