I am trying to do the same thing as you, though not a 29er. Im trying to make a crosscheck-ish bike but with room for 2.1 - 2.2 also. Trying to figure out the best way and what bb to use. I too wanted to go with lugs all around since I am jiggless too. If you are fillet brazing does it matter what bb shell you use? Can u use one of nova's mtb lugged bb shells or will that mess up too much of the other geo? I was hoping not to fillet braze this early on but...

Also what is a good tube set/size for a 250 lbs rider who will be cx racing this bike too? I like OS tubing but mudbay mentioned the unless you are big thing? What chain stays would you suggest, s bend road, zona cx tube set at nova or s bend mtb stays?