Now that I look at the pictures closer, Dakota Boy may be right.
If this gusset is pot metal it is made of zinc which cannot be welded. Zinc is easy to cast and used for emblems and script; pieces that are not used for strength, but more for complex form.
To be honest, none of my classic Ford cars used pot metal in any of the channels. So, I didn't think this piece would be different. Pot metal castings break much easier than steel and I am very surprised to see it used in this location.
If fabrication of this piece becomes too difficult from steel, you may need original replacements from our vendors. (God Bless them.) Having said that and after looking closer at these pictures, I do not recommend repairing pot metal, but it should be replaced with steel.
When welding, it is very important to keep heat far away from the channels and rubber parts. That usually means dis-assembling the pieces first, then welding the parts before reassembly. It really doesn't matter whether your welds used Micro Inert Gas or Tungsten. - Dave