Your "paranoidness" is valid.
If you're not "positively sure that you had a 6M installed, then you'll need to look at the engine ID stamping. Best way to look at is, is from underneath the car.
1. Remove the engine undercover thingy, or at least remove the majority of the bolts on the right side.
2. With a flashlight, look around for the engine stamping marking. It will be in the right side of the motor & it will be to the right of the oil filter mounting flange. It will either say "5M" or "6M" on it.
It SHOULD look like this: (this is from Phil Dupler's webpage, when he was rebuilding/doing the turbo conversion on his 6M).
From the top of the webpage, go about 1/3rd of the way down. OR... Count 23 pictures.... You'll soon see the picture w/ the engine marking on it.
And yes, since you are in Cali, it's more than likely they reused the 5M intake plenium, so that the EGR hookups can be reused, so that you can pass emmissions inspecions.