Big Block Truck Headers/Exhaust manifolds

IIRC my 318 has a rear pickup and pan. How can you tell which end is the front or rear on a big block oil pan?

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Rear sump BB pan will have the drain plug on the back of the sump. BB pan bolting flanges being square with the exception of a divot on the front passenger side. Here's an example from a 187 pan.
I may have a pan & headers also if needed.

PAN.jpg