Rear axle
Back in the day, I went on a weight reduction diet for me and my car. I replaced every non critical strength fastener with aluminum ones. Got pretty friendly with a marine supply place. I lost about 75# with lite weight parts including a home made aluminum radiator support and fender tubs. And I lost 25#, so total was 100#. This was before fiberglass parts were available for my car. The car and I both felt better, I think. Wish I could lose those 25# again now.