I was looking into this for my last 57 about 5 years ago. If memory serves, I had something like 6-7 inches of total travel at static ride height. Taking 5 out leaves almost nil for travel. You may get away with it for a cruiser, but don't expect to haul anything. You will bottom out frequently already.
You won't need a C-notch unless you flip the axle on top of the springs, which will net you about a 6" drop, for free. Problem is, you still are left with about an inch of travel. In comes the C-notch. With proper bracing they work fine. There is a posibility you may have to raise your bed floor to clear bracing, depending on how you do it.
Devin
