Blocks are the old school way of lowering on leaf springs.The alternatives are re-arching the spring or reversing the eyes. Be aware of the departure angle.
For the front deflector, you could look for Hersbird's Hi-Lo as a built example, but he worked from this sketch that I can find:
This represents a pickup camper, as I was trying to resolve the cab/camper gap, but I added it to the overhang as well, as a means of adding a radius without cutting into the structure.
The [rule-of-thumb/first approximation] is 4% of overall width -- or 2" radius or 4" bubble on four feet of width. With CFD or a wind tunnel you might find that capping the pilasters with Batman ear vortex generators that create a central jet down the center of the roof.