Trimmed the main rib that fits onto the horn with the pneumatic dremmal cutter. Nice tool! Don't know how else this was to be done without minimum damage to the rib. Don't get a opportunity to practice on those off-cuts as Christiaan collects them all!
Christiaan and Carla helped removing the plastic of the ribs - there are 5 ribs so they had to share the last one to have equal opportunity to help. Christiaan received a blow in the face when Carla's peace suddenly released. Only the first time though!