The Mopar 10,000 Day Calendar is a 4 digit stamped identification number on the Engine and Transmissions that informs you of the EXACT DATE it was assembled.
Typically production Model Years for Dodge & Plymouth would be from August 1st to July 31st.
Location of 10,000 day date stamps:
Slant 6 (198-225) = Right (passenger) side of block near coil mounting bracket.
Small Block (318-340-360) = Left (driver) side, front of block just under cylinder head
Big Block (383-440) = 383 Below Distributor / 440 Front of the valley pan (Date only, no 10,000 stamp)
Hemi (426) = Left (driver) side of block under the starter near the oil pan flange.
Automatic Transmission = Left (driver) side above oil pan
Manual Transmission = Right (passenger) side on VIN pad.
(Some early Big Blocks got stamped under the starter on the flange like the Hemi’s)
Engine Assembly Plant Codes:
M or PM = Mound Road, Detroit, Michigan Plant (318-340-360)
W = Windsor, Ontario Plant (318-340-360)
T or PT = Trenton, Michigan Plant (198-225-383-400-440)
MN, NM or MV = Marysville, Michigan Plant (426 Hemi)
Transmission Assembly Plant Codes:
PK = Kokomo Plant, Indiana (Automatic Transmissions)
PP = New Process Gear Division, Syracuse NY (Manual Transmissions)
Decoding Additional Symbols & Stampings:
A = .020″ Oversized Cylinder Bore
B = .010″ Undersized Main & Rod Bearings (Oversized Bearings)
C = Special Crankshaft & Pistons
E = Cast Crankshaft
H = Standard 4 Barrel Carb
HP = High Performance
LC = Low Compression
OS = .005″ Oversized Valve Stems
P = Premium Fuel Recommended
S = Service Engine (found on Warranty Blocks)
sP = Special Engine use Premium Fuel (found on T/A 340 Engines)
WT or TW = Water Tested (normally found on Hemi’s & Warranty Blocks)
X = Oversized Valve Guides
2 = Second Shift
♦ = .008″ Oversized Tappets
✠ = .001″ Undersized Crankshaft Journals (Oversized Bearings)
✠+X = .010″ Undersized Crankshaft Journals