[TX '90 ZR1]

In the early 90's there were 2 testing standards.
On the radiator shroud there should be a decal that will indicate if the car was tested to CA. emissions. This will be the easiest if the decal is still there and readable.
Next would be an indication on the window sticker showing a line item charge for the CA. emissions test. Some vehicles required additional emissions hardware to pass the CA. standard. I do not believe the LT5 required anything additional.
Not sure, but I would assume the test standard would be on the build sheet also.