I know this car as the ‘1963 Alfa Romeo Giulia Spider prototype' with S/N 105.03*00002.
The history of this car is also not clear to me.
Type 105.03 is the type designation for the … 1600 Spider (Duetto), but that car (production version) only appeared in 1966.
The Giulia GTC is type 105.25
My theory of this car is that it started as a Bertone design proposal (see picture 1 and 3 I added in my post), and that Alfa Romeo Centro stile ( E. Catoni) modified that car later on (front and rear, but keeping the rest. So also the dashboard which might explain the presence of the Bertone logo).
And that in the end, it was rejected in favor of the Pininfarina proposal.
I added also another design proposal from Catoni (picture 2).
Back in the days, modifying showcars/prototypes happened all the time (look at the Alfa Romeo 2000 Sole, Alfa Romeo 2000 Sestrière, Alfa Romeo 6C 3000,… ) so my theory might be correct, but it is just a guess.
@ Carnut, can you please PM me the website where you found your information?