came across this
1964 Codes:
First Digit = Car Line
1 – Plymouth Valiant
Slant-6
2 – Plymouth Slant-6
3 – Plymouth V8
4 – Dodge Slant-6
5 – Dodge 880 V8
6 – Dodge V8
7 – Dodge Dart Slant-6
8 – CHRYSLER V8
9 – IMPERIAL V8
L – Dodge Dart V8
V- Plymouth Valiant/Barracuda V8
Second Digit = Model
1 – Valiant 100, Savoy, 330, 880, Dart 170, Newport, Custom.
2 – Belvedere, 440, 880 Custom, 300, Crown.
3 – Valiant 200, Fury, Polara, Dart 270, New Yorker, LeBaron.
4 – Signet, Sport Fury, Polara 500, Dart GT, 300K, Barracuda.
5 – 100 Wagon, Savoy Wagon, 330 Wagon, 170 Wagon, Newport Town and Country.
6 – Belvedere Wagon, 440
Wagon, 880 Custom Wagon.
7 – 200 Wagon, Fury, 270 Wagon, New Yorker Town & Country.
8 – Taxi, New Yorker Salon.
9 – Police.
0 – Fleet.
Third Digit = Model Year
4 – 1964
Fourth Digit = Assembly Plant
1 – Lynch Road, MI
2 – Hamtramck, MI
3 – Jefferson, MI
4 – Belvedere, MI
5 – Los Angeles, CA
6 – Newark, DE
7 – Saint Louis, MO
Last six digits are the sequence number