Originally Posted by http://www.type2.com/m-codes/t2chassi.html

The Chassis number (1970-1979)
Busses of model years 1970 until 1979 have a chassis number that consists of 10 digits.

The first two of them are not displayed on the option plate, but you can find them on your registration papers and in the back near the engine. These two numbers indicate the model:

21 Van (no windows in cargo compartment)
22 Microbus
23 Kombi (windows in cargo compartment)
24 Microbus Deluxe
26 Pick-up
27 Ambulance

The third digit (the first on the options plate) stands for the model year. For example "7" stands for 1977. The model year runs from August of the previous year until July in the actual year. So Model year 1977 started in August 1976 and ended in July 1977.

The fourth digit (the second on the options plate) is a "2" on all busses. I have no idea why.

The number that remains is a serial number.