Andy, sorry to see this happen, scares the crap out of me to see that...
Just from what I see there, I would get it back into place, do the repair weld (which will probably be better than the MMC welding) and add a longer pin similar to the clutch pedal.
You can have it removable so it just slide through from the left and is caught within both sides of the brake pedal as well as the pivot point for the master cylinder pushrod.
The hardest part would be to get the pedal assembly out of the M3W. Making a longer pin would not be that hard and drilling the pedal sheet metal with the two extra holes would be a breeze when the pedal is out being welded.
My thought would be that the weld "should" be enough, but as a fail safe, the longer pin would just be an emergency backup.
Or update the new style pedal assembly.
