VIN Plate for 1972-80

The VIN was located on a plate visible through the windshield on the driver’s side dash panel.

1st Digit: Division
2 = Pontiac

2nd Digit: Series
S = Base Firebird
T = Esprit
U = Formula
V = Trans-Am (1972-74)
W = Trans-Am (1975-80)
X = 10th Anniversary Trans-Am (1979)
X = Turbo Indy Trans-Am (1980)

3rd and 4th Digit: Body Code
87 = Sports Coupe

5th Digit: Engine Code
A= 231 c.i.d., 2-bbl V6 (1978-80)
C = 231 c.i.d., 2-bbl V6 (1977)
D = 250 c.i.d., 1-bbl L6 (1972-76)
G = 305 c.i.d., 2-bbl V8 (1979)
H = 350 c.i.d., 4-bbl V8 (1975)
H = 305 c.i.d., 4-bbl V8 (1980)
J = 350 c.i.d., 4-bbl V8 (1976)
K = 403 c.i.d., 4-bbl V8 (1977-79)
L = 350 c.i.d., 4-bbl V8 (1978)
M = 350 c.i.d., 2-bbl V8 (single exhaust) (1972-76)
N = 350 c.i.d., 2-bbl V8 (dual exhaust) (1972-74)
R = 400 c.i.d., 2-bbl V8 (single exhaust) (1972-74)
P = 400 c.i.d., 2-bbl V8 (dual exhaust) (1973-74)
P = 350 c.i.d., 4-bbl V8 (1977)
R = 350 c.i.d., 4-bbl V8 (1977)
S = 400 c.i.d., 4-bbl V8 (1975-76)
S = 265 c.i.d., 2-bbl V8 (1980)
T = 400 c.i.d., 4-bbl V8 (dual exhaust) (1972-74)
U = 305 c.i.d., 2-bbl V8 (1978)
W = 455 c.i.d., 4-bbl V8 (1975-76)
W = 301 c.i.d., 4-bbl V8 (1979-80)
X = 455 c.i.d., 300 hp 4-bbl V8 (H.O.) (1972)
X = 455 c.i.d., 4-bbl V8 (Super Duty) (1973-74)
Y = 455 c.i.d., 4-bbl V8 (1973-74)
Y = 301 c.i.d., 2-bbl V8 (1977, 1979)
Z = 400 c.i.d., 4-bbl V8 (1977-79)

6th Digit: Model Year
2 = 1972
3 - 1973
4 = 1974
5 = 1975
6 = 1976
7 = 1977
8 = 1978
9 = 1979
A = 1980

7th Digit: Assembly Plant
L = Van Nuys, California
N = Norwood, Ohio

Last 6 Digits: Sequence Number
Sequential production number starting with 500001 for all 1972 models and 100001 for all 1973-80 models.

Note: All VIN information is courtesy of YearOne Inc.

How can you tell what number your car is in production.

Last 6 digits. In 1972, the first car produced was 500001. For the years '73 - '80, the first car produced reverted to 100001 each model year.

If you go to Gary Lisk's source pages, you can look up the total production numbers for each year. Excellent reference material:
http://www.2gta.com/

The date code on the block and heads can give you an idea of the relative production date, but keep in mind that engines could sit around for a while awaiting their turn to be used on the production line. Also, if the block or heads have ever been switched, that kind of negates the test.