Steve,
I haven't posted in a while and thought it would be a good time. Sorry to hear about your shackle problem. I thought Montana had a good handle on this but from the looks of your shackle they have went backwards a little.
My 2000 with 8 inch frame had Montana Service advisory 008 installed and I thought it was good engineering. I was sorry they didn't carry through to the 10 inch frames.
The mod included a two inch rectangular bar welded to opposite shackles. 3 total. Then the four end shackles had three rectangular braces welded to the shackles.
The original shackles had a brace inside the shackles which is missing from yours Steve. ????
First pix shows two of the triangle braces.
Second pix shows the OEM brace that you don't have and the third triangle brace. Also shows the 2 inch rectangular steel bar beteen shackles.
Third is just another view of the second pix
Maybe Montana will see this and re-enforce the shackles.