I haven't seen the other car but it might be easier to transfer the mechanical parts from this car to it.
Bill

If there is actually any sheetmetal under the rust, you might try mig. If you want a wire that is alright at getting through rust, then try flux cored wire. You still have to take off most of the rust, but it is good at getting through a little bit of dirt or rust.

I would try to replace the parts, before I tried to weld on them. If you can't replace them then I would clean them up as best as you can, and try the mig.

Make sure you have thick enough metal after you remove some of the rust. If its paper thin watch your temperature when using the mig or youll do more damage than good if you burn through.