Actually, you have it backwards!
The inlet is at the opposite side of the motor. The air flows back-wards through the blades of the wheel. You know that part.
In my setup, the blower sucks air from the front, and blows it back towards the heatercore. The shroud I've build leaves a 1/2" gap around the blower's mounting plate (minus 5 screw tabs), for the air to get to the heatercore.