Which oil pan for a 318 magnum swap?

I'm putting a 318 magnum from a truck in my Dart and I bought a car pan for it but the pan doesn't seem to fit. The back end of the pan seems to be bigger around the main seal than does the original truck pan-leaving a 1/4 inch gap. What kind of pan fits the magnum motors for use in cars?
I've heard you have to use a 360 LA pan for the 318 magnums.
anyone?
Al.