1972 california commercial license plate.

[desert-rat]

So for us Californians trucks are registered as commercial and have different plates.
For a passenger vehicle in '72, the format would be
123 ABC. My '72 C10 format is 1A12345 on blue plates. My question is, is that the correct format for a '72 truck??
I tried researching DMV and on line. Can't find anything. How far back did commercial plates for pick up trucks go? I know that the letter can be elsewhere instead of the second character on the plate.