I'm interested in building this. The internal crosspiece will carry a huge load. Questions:

1) How far up the mast is the internal crosspiece?
2) Is that crosspiece really "Z" shaped? What is it made of? How thick is the stock material?
3) How is this crosspiece connected to the mast, rivets or a bolt all the way through?
4) The drawing is just a schematic. In reality, could one or two of the internal blocks be a double or MUST they be 2 singles to achieve the cascade effect? First, the 2 on the crossbar could certainly be a double, right? Although only one single is shown for the blue, there must be another that is not shown. Could that be a double? That one might be too close to work as a double, space wise. Hmmm... Wout?