Good luck. I had 4 of the 6 inserts go on me. I ended up cutting it all out (the whole bottom of the frame along the inserts), treating the inside of the frame, and then making two 30" long custom frame caps out of 3/8th steel (3" high) with welded in nut inserts. For the nut inserts, I welded in wheel lugs from German cars for the nut, and I use Japanese lug bolts to hold the pan in place. The frame caps were then welded into place. It worked great.
Here it is after being welded in, but before paint.