Do the frame notch/welding first. The sway bar floats on the busings and doesn't really hold the frame in alignment side-to-side. I notched my frame and fully welded it before installing the sway bar. You run the risk of binding up the sway bar if you weld it first, then the frame as the frame might move/warp slightly was it is being welded. Weld the frame, let it move any that it may, then put the sway bar in.
good luck
Todd