I have 2 inch lowering springs and 255-50-17 tires (27 inch) on the back. My ride height at the frame is 4 3/4 inches. I have done nothing other than put the springs in, and the tires on. The shocks are Bilsteins. I do not know what length they are, because they came with the car.
Did you remove your shocks? The shocks may have reached their full compression, although that does not seem correct. I can not imagine both shocks being broken at the same time, so maybe someone put the wrong shocks on the car.
I do not know if anyone had used coilovers, but since the lower mount is not boxed, I would think it would have a tendency to bend with the coilovers. Most people who lower the cars just use drop springs, or bag them. If you are using drop springs, weld a 3-4 inch piece of tailpipe to the upper spring perch, and tiewrap the spring to the lower to keep the springs from falling out when you jack the car to change a tire.