Lightening your K frame

I wouldn't bother trying to save weight on the k member. What are you going to lose? My guess is 4 pounds max. Not even worth it in my opinion.
Actually, you would be better off welding all of the seams solid and fixing the crappy factory welds that they all have, and then putting on extra gussets to strengthen it.
This is actually my next project as well!
That's what i am going to do to mine.