I always had my doubts about the special characteristics my car had. After a lot of searching and asking I finally found multiple tables which I concentrated as you can see below and after comparing them with other information I had, I suppose they are as much complete as they can be.
 
Take your time and give them a look. They might solve all your questions.
 

Ghost Sketches, Suspensions

Official Drawings - Brochures
 
Dimensions

Old and new Boxers

Compact Table

General Technical Information Table

Maximum Speeds

Acceleration

Braking Ability

Fuel Consumption

Oil Consumption

Total Weight and Distribution of Weight
 

Personally I think you should buy the book by David G. Styles, "ALFA ROMEO SPIDER, ALFASUD & ALFETTA GT, The Complete Story", Ed. Crowood Autoclassics, since it's the source with almost all the information you gonna need about this car. All my other sources were magazines (which I spent a hell lot of a time trying to find them), Alfa Romeo's official brochures, my car and a friend's car and knowledge (Thanks Gannino!).