BB K-member Weight OEM vs DC
The DC K-member is a modified small block K-member with a little more metal added that really wasn't necessary. BUT, the late K-member does have two large holes in the bottom that probably lighten it a bit. I have my '68 small block k-member out of the car and a stock '73-up k-member out of the car. If I think about it in the morning I could weight them.
As for lightening the front end, there is little that can be done short of cutting out lots of sheet metal, which still won't add up to much. I've got an inner fender up on the shelf, but I don't think it weighs that much. Fiberglass fenders, hood, bumper, and doors will do more. Many years ago my family stopped by Larry Gilley's place. He was trying to lighten his '68 340 S notch by drilling lots of 2" or so holes all over the front end. I don't think it was more than a pound.