Answers you prolly wont like...
At the very least...
You definately need to upgrade to the larger bolt size, drill and tap the frame or whatever is nessecary. Good chance to go to some grade 8 stuff.
If you are getting rid of the torsions alltogether and the shock is taking all the weight now, they should not be set up in single shear! That is a huge no-no on anything carrying any load. BUT, I know everyone is doing it anyway, its just not safe.
Here's a pic of how I modified some front arms to be double shear...
Hope this helps?
Jeff-