About the yellow clamp: That is what I thought also for the first time, that it had to be the angled top plate, but then: in this picture and also the other picture where the back is also glued on, the angled plate is not angled, but 90 degrees to the front baffle and also it is above the tweeter and not between the woofer and tweeter. So is it there just to have the front baffle exactly at 90 degrees to the side wall (that is on the bottom)? As a support and not glued, just fixed with the clamp?
I am not a woodworker nor is it my profession working with wood, it is just I want to get it right and for that there is one chance to get it right. So the saying "measure twice, cut once" applies for me very much, even if in this case "measure twice, glue once".