(The reason the clutch came loose was that I tried to open the machine so I could tighten up the starter cord. Doing that compromised the clutch's retainer. Although I tried to improvise something, it did not hold.)
Step 1: A better clutch retainer
Step 2: Where to mount an improvised clutch housing
Step 3: Clutch housing mounting tabs
Step 4: The "L" tabs for mounting the improvised housing
Step 5: Wood block
Step 6: Drill a hole for the boom
Step 7: Saw the block into two halves
Step 8: Finished
In this photo you can also see how a hole was made to accommodate and fit the throttle cable.
I have used this weed trimmer for more than ten years since making this repair and it has been as good as factory new. While the clutch now runs in open air inside the steel "L" tabs, it would be near to impossible to acquire an injury from the spinning clutch. You might never need to make this repair, but what I did might provide an idea for you for something you will need to do.