I recently bought a used strut tower brace and firewall supporting bracket for my 2017 base model GT (First attached picture).
The ebay listing said these were taken from a 2016 Mustang GT. The smaller third bracket, I have no idea what it's for or where it would be used on a Mustang. I did web searches for the "FR3B63016A52A" and couldn't find anything that described this part.

Can anyone give me an idea what this bracket is for and where it is used?

Below are pictures of the front side, back and close up of the three part numbers on it.

Thank you,
Merril

Ebay listing picture

Mystery bracket front

bracket back

bracket part numbers

 

Did you ever figure out where the bracket goes?

 

I did... GOOGLED it, so dunno how he missed it...