Update: I weighed the bumper as you see it below, it’s 9.2 kg (20.3 lbs). For comparison, the stock chromed steel bumper, minus plastic end caps, weighs in at a svelte 5.6 kg (12.3 lbs)
A little progress made on this project. Made up a more or less matching end cap and also did some preliminary grinding out of the welds. What a chore this way of making a bumper this is. You understand don’t you, that this is me making it up as I go along, modelling (I can hardly say sculpting can I?) a bumper out of aluminum plate. Once I get a shape that I like and that works then I can take measurements and think about how you could make one easier and faster.