There are a couple of ideas that other builders have used. One is to use rectangular tubing for the diagonals in the fuselage. Maybe 1inchx2inch. And do not stagger them like the original round tubes. Instead the center line of the diagonals should intersect at the center line of the 2 inch tubes (proper practice at joints).So let’s think, what would you folks change, but with the same soul of the Affordaplane?!
Gusset plates with rivets at the joints is another idea. Would be lighter and easier to build. You won't have to drill all the way through the 2 inch tubes. It could be riveted flat on the table, flipped over, and the other side riveted (plans say to elevate it off the table for drilling and bolting).
And, erkki67, your picture showing the top longeron going to the wing is another idea I have seen. Also there are ideas for improved landing gear.