Classic/Antique Car Repair: 72 el camino VIN#, sequential number, question thanks

Question
QUESTION: I have a 1972 el camino the brake combination valve has a push button on it. What exactly is this for.

ANSWER: There is a spring clip that is supposed to be used to hold that valve open when bleeding the brakes. It supposedly neutralizes the valve so that the pressures are equal and unrestricted in each end of the vehicle for bleeding.
Brad

---------- FOLLOW-UP ----------

QUESTION: Thanks for reply on the 72 el camino combo valve.I was also researching my vin# (complete runaround)and was wondering if you could help or steer me in the right direction ,it is 1D80H2L533618 also what is the tag on the cowl. Thanks Again.

Answer
Ok, here goes.
1= Chevrolet
D= Sales Code
80= Body Style ElCamino
H= Engine code
2= Model year
L= Assembly plant Van Nuys Calif.
The rest is the run or unit number called the Plant Sequential Number. The key to this can be found in a Chevrolet Factory Service Manual. Also for more information go to web site http://www.nastyz28.com/decode.html
Brad