Last thing for today.
Cut the 'polycarbonate' sheet into two new access flap cards for the side curtains. I don't know what the difference betweeen perspex & polycarbonate is, but I have been assured it is very much stronger and long lasting.
I drilled two holes in each flap, where the corresponding metal piece is on frame, and glued two magnets into the plastic. By pure good fortune, the magnets are almost exactly the same thickness as the plastic sheet. They are just a tiny bit narrower, so the holes I drilled were not all the way through. That way the magnets can't be pulled out of the plastic.
With these bits finished, and reference photos printed on Saturday, all pieces can now go to the Auto Upholsterer tomorrow afternoon.
I have been advised it will take about 2 days to make the new curtains.