I always wanted to do that with my (dear departed) 240! In the end I was able to make quite a nice looking repair using aluminum riveted and then heavily sprayed with undercoatng to close the very large gaps at the back inside of the wheel arch, with hardware cloth and bondo to do the bits that needed cosmetic sculpting. Ample sanding, application of "ruststop" and then primer seemed to hold the rust in check. The car looked great from the outside though the bondo extruded through hardware cloth looked rather strange from the inside. The repair was still looking good when I gave the vehicle away some years later.