****.Me
That's some bad fapping rot - and that D/S plate haning in mid-air is scary, too - you'll need to get some decent plate up in that area - is that rot above the spring hanger aswell dude ?
Just replace the ****er. I seriously doubt your going to find ANY good steel to weld to under there to get a good patch - and if you do, it'll probably be so bloody thin, it'll punch through. it's tempting to try and save some moolah - we've all been there - but if it's that far gone you'll be wasting yer time with patches.
You'll just need the "normal" x-member (not the military one) Question is, though - you'll need to chop the old one off at the point it meets the chassis legs, and the new one slots over where you've cut - What condition is the steel in that area - worth checking with a wire brush and a big ass screwdriver