I believe there are a couple of things that some of the gurus on this site know from experience that are giveaways as to true SS or not
These things will most likely not be published on the forum or on the internet as they are sort of the last things left to tell a fake from an original
I agree in keeping some things close to the chest as these cars are rare and there are many out there that would like to and have the money to clone one for their own gain from an unsuspecting buyer in the future
Without the original build sheet and all the paperwork for the car you can only go on what you see on the car and with a bit of help here you can get closer to knowing for sure.
Good luck, i would love to have an original SS but over here there are more badged SS 61 impalas than non SS impalas so i will keep mine the same as it was born.