A shroud on the back with an electric pusher on the front will do absolutely nothing. The shrouds on the backside of radiators are designed so that the rear mounted fan is pulling air across and through the entire surface of the radiator. Without a shroud a puller fan will just pull air from in front of it in general, which may not be just through the radiator- it can pull air from around the radiator in the engine compartment. The shroud is to force a puller fan to pull air through the radiator.
A shroud on the front of the radiator will block incoming air through the radiator, which isn't what you want. The fan is pushing air through the radiator, and just pulling air in front of it. A front mounted pusher fan should have a "ring" around the outside of the fan blades to keep air from escaping out the sides. In theory it may also recirculate some air from behind the radiator back through if there's no shroud, but, the point of the pusher fan isn't to evacuate air from in front of it, it's to push air through the radiator. The air resistance created by the radiator itself would also keep to a minimum. And the moving air blocked by a front mounted shroud when the car was moving would be more detrimental than any slight improvement from eliminating any possible recirculation when the car was sitting still at idle.
