Nothing is definitive,you have to look at the sum of the results.VIN# won't tell you if it's a Super Sport,but you know that.
If the rearend is authentic to this Chevelle,what is the suffix & date code on the passenger axle tube?
Transmission suffix too if it has.
Round gauge dash cluster?
Is there a Tach..redline?
Did you remove the engine compt.heater box to look for a VIN#?
Also aim for the frame rail over the Drivers side rear wheel.Sometimes that and the complete rear Frame rail running parallel to the rear Bumper will show a VIN#,but the Body has to be off the frame to find these.
Look at the steering shaft.Does it have a removable connection into the box,or is it solid?
Another indicator,if it had a Flapper SS hood,look at the Firewall behind the coil,(Better diagram in ASS. Manual),for a hole where the Cowl induction relay would have been mounted.
There are so many things to look for,can't list them all in Detail here.