There will be no gain in making the fans fight each other for the airflow direction. You will want the electric fan to assist the mechanical fan in pulling the outside air into the engine compartment. Sounds like you have other over-heating problems anyway. Have you flushed the system? Maybe take the radiator out and see if you can flush any nastiness out of it.

1953 Chevrolet 3600
Fried Green T'mater (Vern)
In the Stovebolt Gallery
Caution: Political Statement
Man who runs in front of car gets tired, man who runs behind car gets exhausted.