I fabricated my centerlink from hollow chrome-moly tubing which we plug welded and seam welded all around to the original link ends. Saved 3 lbs.
Thumper.
You can use thin gauge sheet aluminum for the door panels and use a good industrial glue to adhere the panel material. Magnesium is prone to being flammable, a no no for interior work.
I've also fabricated the top portion of the door panel out of aluminum. The originals are slightly heavy steel stampings. saved about a 1-1/2 lbs.