rr504. have you seen the homemade "xtracycle" on the indestructables website? (i think). I think thats also the one that oldfool is refering too. It in braced down by the bottom bracket area. I'll try to find the link for it and edit this post with it later.

Other then that, it looks good! But please dont get me started on wanting to build one of those I allready have 5 bikes in the living room now!