Thanks for the replies so far. I'm looking at a set of wheels with Shimano XT hubs and Mavic A719 rims in a 40 rear, 36 front. As far as speeds are concerned, I haven't given that much thought. Everything on ebay seems to be 9 speed cassettes. I want a 34 or 32 tooth large sprocket for my granny gear up front.
I think going to 26" wheel would lower the bottom bracket too much and force me to move the canti-posts and then repaint the frame.
I guess I was hoping for a fairly easy swap--that hope may be fading.