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From this site, "The remaining six digits indicate the sequence number (serial number)":
http://www.degeneratepress.com/newport/vin66-74.htm
1968 Codes:
First digit = car line
B - Plymouth Barracuda ("A" Body)
C - Chrysler Newport, 300, New Yorker ("C" body)
D - Dodge Polara, Monaco ("C" body)
L - Dodge Dart ("A" Body)
P - Plymouth Fury, VIP ("C" body)
R - Plymouth Belvedere, Satellite ("B" body)
V - Plymouth Valiant ("A" body)
W - Dodge Coronet ("B" body)
X - Dodge Charger ("B" body)
Y - Imperial Crown, LeBaron ("C" body)
Second digit = Price class
E - Economy
L - Low
M - Medium
H - High
P - Premium
S - Special
K - Police
T - Taxi
Third and fourth digits = body style
21 - 2 door sedan or coupe
23 - 2 door hardtop
27 - Convertible
29 - 2 door sports hardtop
41 - 4 door sedan
43 - 4 door hardtop
45 - 6 passenger station wagon
46 - 9 passenger station wagon
Fifth digit = engine
A - 170 1-1BBL 6 Cylinder "G" engine
B - 225 1-1BBL 6 Cylinder "RG" engine
C - Special Order 6 Cylinder engine
D - 273 1-2BBL 8 Cylinder "LA" engine
F - 318 1-2BBL 8 Cylinder "LA" engine
G - 383 1-2BBL 8 Cylinder "B" engine
H - 383 1-4BBL 8 Cylinder "B" engine (High Performance)
J - 426 2-4BBL 8 Cylinder "RB" engine (Hemi)
K - 440 1-4BBL 8 Cylinder "RB" engine
L - 440 1-4BBL 8 Cylinder "RB" engine (High Performance)
M - Special Order 8 Cylinder engine
P - 340 1-4BBL 8 Cylinder "LA" engine (High Performance)
Sixth digit = model year
8 - 1968
Seventh Digit = Assembly Plant
A - Lynch Road, Michigan
B - Hamtramck, Michigan
C - Jefferson, Michigan
D - Belvedere, Illinois
E - Los Angeles, California
F - Newark, Delaware
G - St. Louis, Missouri
R - Windsor, Ontario, Canada
The remaining six digits indicate the sequence number (serial number)