(I haven't gotten official information about this car, so I am going by pictures, but...)
The spyder and coupe have different wheelbase's.
The 90th anniv spyder has most of the bodywork from the GS, but with special tags, serial numbers, etc. The 90th also has the special carbon fiber convertible cover that doesnt look like its on this GS spyder. The 90th is also missing the lip spoiler on the trunk lid.
The interior of the 90th anniv is essentially GS, in specific colors.
The 90th anniv car does not have the GS specific tuning - for engine, transmission, or suspension.