Mac cut out the shape for the seat out of his sheet of 4mm ally and then drilled the holes for the rivets and the retaining bolts for the seat springs and pivot bracket. He had a go at manually bending a ‘lip’ at the back but even 4mm ally is incredibly strong and resistant to bending …. so off to Heisenburg to beg/borrow/steal the use of his machinery to put a nice radiussed  bend in it to hopefully prevent the rider sliding off the seat under acceleration. Plan is then to sit back and decide how hardcore we want to be………………….. polished ally with brass rivets or foam and leather……………. may require a few miles on the clock before we visit that question (and later the chiropractor).