Hmm, so perhaps I could use something like this Henry James Cleanline Mountain Bike Shell: http://www.henryjames.com/productmtn.html#mtn and fillet braze just the chainstays while keeping the rest of the bike lugged.

Given that a 29er kind of throws the classic handbuilt bike look out the window anyway I'm mostly trying to build with lugs because it seems easier to jig.