Rule #1 - slow down on the speed bumps and any other obvious dips in the road like at intersections. 3" of ground clearance is enough at the bell housing (but obviously not in the case that is shown in the photo). It looks like the driver hit a significant dip (or bump) at speed to cause that kind of damage.
With regards to the
oil pan. I had a 9 quart
oil pan on my 392 Ford Racing Motor that I had scraped twice in the first two months of ownership. Resulted in small leaks in the pan that I had to repair. I would estimate that I had 2" to 2 1/2" of ground clearance on that pan. It was ridiculous - protruded way below the frame rails of the car. Finally opted to swap it out with an Aviaid 7 qt
oil pan that gave me an additional 1" of ground clearance. Now the bottom of the pan sits at the same level of the frame rails and have not scraped it since. Nice looking pan too. Its a relatively easy swap. I did have to change the pick up as well since the new pan was shallower but that was provided with the pan. Would highly recommend Aviaid pans -well designed and look great.
Don't lift the front of the car by adjusting the coilovers just to get additional ground clearance for the pan. You'll start distorting the stance of the car and before you know it, you'll end up with large gaps between the top of the front tire and the fender. Will look very stupid.
One other piece of advice. If you do decide to swap the pan, then ditch the pan bolts and replace with studs. Makes re-installation alot easier when all you have to do is install the pan over the studs and then screw on the nuts.