Can you expand the center holes REAL LARGE---like air frame members or steam punk stuff?
That can drop the weight a bunch. Can you rivet on the support pieces from Al?
You can get a quite shiny surface by buffing with a sisal buff and black compound, the better the surface you start with the faster it goes.
WARNING: Buffers are machines that stay up all night thinking up ways to *MAIM* their users so BE SAFE! (I believe that more knifemakers have ended up in the ER through buffers than any other tool in the shop!)
WARNING II: Even as an untempered mild steel or Al display only piece it is not a toy and you can quite easily hurt yourself or others goofing around with it---even with a very dull edge. So take care; hurting your friends is counter productive, (hurting yourself is just stupid!)