The only way to tell a 69 SD as there are very few of them ,....is a GM buildsheet or also the GM Historical services documentation from George Zapora.....easily available on every GM sold car in Canada

The car would have to be a 734-series, should say L35 or L34 on the trim tag, along with the transmission RPO code (MC1, M20 or M40). I can't recall but I would expect it to also say Z25 on the trim tag.

If you don't mind paying, VVS can tell whether the v.i.n submitted is for an SD or not. We are so lucky to have that service here in Canada.

Below is a picture I took of a real SD-396 back in 2011. It belonged to former member 68SD. He was getting ready to leave so I couldn't get a photo of the trim tag.

 

I used to have a bunch of photos from the Northern Chevelle Gathering in New York from 2005 where there were actually THREE 1969 SD-396s (2 real & 1 perfectly done clone). Unfortunately I didn't have them backed up yet when the drive partition took a dump. 2 red ones plus the green one above.

As a car spotter since the late 60s and remembering Beaumonts new, the  SDs in 2005 were the first '69s I had ever seen. Super rare. I've actually seen more COPO Chevelles than '69 SD-396s.

Here is a pick of Bills car wagon64sd. This is a real sd also. Not sue if the car above is the same car as Freds 68sd car looked the same but was born a custom and cloned into a SD.