Thanks Tom,
The only real design changes I made were moving the rear blade perpendicular to the sides instead of leaving it angled like the front one and turning the rear blade straight up and down instead of laying it back at a 45.
Those two changes were made because all my roads are dirt...dirt... and more dirt. There's no gravel anywhere. The one time I used it on a graveled parking lot, it performed very well the both blades angled and tilted. But since the majority of its life will be spent grading my dirt roads, those changes were necessary.
The dirt we have around my place is called "sugar sand" around here. So the front blade with it's 45* angle cuts 1/2 below the surface and the dirts spills over. The rear blade comes along and acts almost like a box blade to smooth out the now loose sandy dirt and distribute it evenly.
Hope this helps.
Mark