I also had cracks and re-riveting problems (heads popped off), even with the doublers.  I was told that bucked rivets are stronger than squeezed rivets.  I even had the backplate cracks welded for temporary flight use and those cracked in 20 hours.

 

Last year I bought a polished aluminum spinner replacement from Aircraft Spruce that works with the Hartzell compact hub constant speed prop on my 320.  3/4 inch can be cut off the back for a better fit and I had to cut my own forward bulkhead.  I also purchased the Lancair doubler plates for the supplied backplate.  While this was a lot of work, I am very pleased with the result and it is rock-solid with the bulkhead.  I don't think I will see cracks in the backplate anymore.