Max_75, there are scores of fabulous books out there on these cars, indulge yourself!
Most of the mods listed here were certainly not on every GTA. Items like sliding block, lightweight dashboard, 90 lt fuel tanks, elektron bellhousings and knucklerisers were Autodelta only. There was no elektron differential housing, but there was the elektron tailshaft housing of the transmission! They all had the lightweight seats, however. Standard they came with the crossover air plenum like a standard GTV.
Final Drive ratios were available as 5.12, standard I think, and up to 5.38. There were around 3 flavors of close ratio gearboxes. Heck, the sliding block wasn't homologated till 1966, so I don't think you'll see that in the FIA Appendix K racing GTA's?
I'd love to see what other owner's GTA's weigh. Mine is a fairly standard race car, no interior to speak of and two 3kg seats. Mine has a standard GTV gearbox and radiator, and no elektron, and weighs 1870lbs. dry (no gas, but oil and water). It has a full wiring harness and wipers. It's FIA legal. Alfa Romeo got them homologated to 1650lbs. I'd love to see how they got these cars that light back in the day!