First I made rudder blocks from White pine blocks glued together, because I was not able to get Douglas fir here in Baltics. Later I made blocks from Siberian Larch that is superior to White Pine as well as Douglas fir in all parameters.  Plans call for the following assembly procedure: blocks to tube/ ribs to blocks/ L.E. installation/ T.E. installation.

Siberian Larch

Right angles to drill straight holes for blocks