[lunarhighway]

i'd go for a top grill block first as well, all air entereing there will have a tougher time getting out of the engine bay again the bottom grill is closer to the bottom of the car.
also it will make for a smoother transition to the hood.

if you can get away with a full top grillblock you car start blocking parts of the lower grill.

in any case i'd make provisions for quick removal of the block, or a movable door, in case temperatures go up.

grillblocks are nice, but do some testing, also take into account that for short trips (wich might make up your dayly commute) more grill blocking will be allowed, but for longer trips you might need to remove some.

wheeldams seem to be a good thing.