Dimentions of parts:
C19 and C20: in my opinion they should be 6,8cm (bottom line)
C12 and C13: thats rather hard to say, (1,5 or 1,6cm): I would do as follows: Fold parts 12 and then insert Parts 13 (should be shorter than parts 12) - being in sum 1,8cm - without glueing and the adjustment to...