Should've clarified on the stainless welding it depends on what you're trying to achieve. If you're building a project and the metal just happens to be stainless, you can weld it with a variety of methods and materials. For example, most stainless can be welded to typical steel with the same mig wire and shielding gas used for non-stainless materials......... However, be aware the weld area will rust. If you want to join stainless to stainless and retain the stainless quality of corrosion resistance it will require stainless wire same alloy as what you're welding. With the hassle associated with changing mig wire, I avoid that process by keeping some stainless electrodes for the stick welder and use it on those occasions.

On the radiator issue, another consideration might be epoxy to affix the mounting bracket.