AZ< you have several options here,,,,,
1stly if you are going to do any sort of non ferrous metal brazing rod, then will need to make a slight indentation around the area to be filled or when its ground back it will the weld area will crack .
1, lead is a great filler , and very low heat, set your flame to that fierce bright white , standard panel steel or next size up , apply liquid flux to surface, the very gently melt lead into the affected area,
2, silver solder look for a 50% silver, again needs its own flux, this would be good to use a small piece of panel steel, just have to watch the flame can blow the steel away before your rod does its thing,, you can "prime" the surface with a little s.solder before hand to prevent this. use more of a panel steel flame on your torch.
3, bronze rod .. 1/8 thick, has its own flux or can get a flux coated rod (?)
same flame as above (both work best with about a 1/16th feather to end of the blue cone ) a heat and dab it in just like a mild steel filler rod
4, TIG weld, mild steel filler rod ,, this would rust up like the surrounding steel . low amp would lead to little distortion.
5. low amp mig , just slow fill hole from around the edges,,,
luck crate