Theoretically it could be TIG welded but it is made of pot metal not aluminum so the melting point and strength of materials are dismal. Best bet is epoxy a threaded insert into the louver and use a brass screw into your newly made blind threaded hole, then attach from the back.
To TIG weld it you would need an Aluminum threaded rod (aluminum screw with head cut off) and a hole to insert it into. Because pot metal is a cheesy Zinc based metal with Copper and Aluminum or Lead added to the mix it is difficult to weld (low boiling point close to point of oxidation). Anyway by using Aluminum wire you should be able to braze it in place under an Argon atmosphere if you can keep the heat down. Keep the fire extinguisher handy as it will burn like a flare if ignited, and water only exasperates the problem not put out the resulting fire.
If the louver fits nicely against the fender, you could install it using double-faced adhesive tape available at an auto body supply house. This method would be fine for a daily driver, but may be noticable for a show car.
Those louvers came either completely painted, or painted with a chrome edge. I have one of the completely painted louvers if you are interested.