Hi Rukawa.
You have several methods to know the displacement of your Chevrolet.
1. A possibility is to look at the documentation of the truck.
2. Another possibility is to look at the engine code that has to be in the motor block. And look at the code on the Internet.
3. This is the last option and only if we have the engine disarmed.
Measure the diameter and career of a cylinder and mutify it by the number of cylinders calculating the compression ratio.