Anyone know if a 72 Duster K member will fit in a 74

I cannot tell from your photo, appears relate to the lower control arm pivot pin, which is fairly common. That is a sleeve in the K member and the pin goes in with a nut on the back side, a friction fit so to speak. If the sleeve is not damaged you can clean it up and weld it, I would get some "big ***" washers to reinforce the area. You will want to build a simple "mirror jig" off the other side to get the thing close to alignment. If you do get it imperfect, you can get adjustable strut rods