Here's how to decipher Ford part numbers. As an example we'll use D1ZZ-6675-C.

The first two digits indicate year. The letter is the decade.

A = '40s
B = '50s
C = '60s
D = '70s
E = '80s
F = '90s
G = '00s

The third digit designates body line:

A = Ford full size
D = Falcon
E = Escort
F = Pinto, Maverick, Falcon
G = Early Comets, Montego, Cyclone
H = Medium/Heavy Duty Truck
K = Edsel
L = Lincoln Mark VII
M = Mercury 
O = Fairlane
R = Capri
S = Thunderbird
T = Pick-up Truck or Bronco
U = Econoline Van
V = Lincoln
W = Cougar
Z = Mustang 
{there are actually many more}

The fourth position signifies the Engineering group

A = Chassis
B = Body
E = Engine

If it is a Service Replacement part the designator will be:

Z = Ford Division
Y = Lincoln-Mercury
X = Original Muscle Parts program
M = Ford Motorsport, SVO, FFRP

The center number, four or more numbers or letters, is the part number. The A at the end of the number indicates that the part is the first version. If it was revised once, it would be B. If it was revised again, it would be C, and so on. When they run out of letters, it becomes AA, AB, and so on.
So if we decode this number, D1ZZ-6675-C, we come up with the following:

D1 = 1971 model year
Z = Mustang
Z = Ford Division Service Replacement part
6675 = the group number for oil pans
C = The third version of this part




- macx