From the head of the bolt #1 to the split is not threaded.
The "Back half" as indicated by #3 is threaded, so no nut.
When the bolt is tightened, it pulls the front closing the gap at the split.
The "tab" indicated by #2 indexes the strut into a notch in the bracket.
Head missing off bolt will cause the split to open up and the strut to move in the bracket.
All the load of the car will be on that little tab every time you hit a bump.
Drill out the broken bolt, if you damage the threads, use a longer bolt and nut to clamp it back together.
Member #437 FIREM
Club Secretary Serving on BOD for 15 Years "Fotki Captain",
25 Years of the LH
20 Years Club History
20 Year Celebration of the Special
https://www.300mclub.org/20th-anniversa ... m-special/
Other Projects: viewtopic.php?f=60&t=36818