That's a wonderful story and I hope this little gem will be back on the road someday!
While I am really fond of these etcerinis, I am afraid I am no expert and won't be able to add any sensible information to the discussion.
However, I did some -out-of-the-box- thinking and here are a few comments and possible leads that might revive the discussion:
- Looking at the pictures of your car it looks like it did not bear any insignias like can be seen on the picture from the Ruoteclassiche (first one above the front wheel arch, second one between the door and the rear wheel arch -a SIATA ‘V-shaped’ badge if I am not wrong-). Question is: can you check if there are holes on your car?
- Generally speaking, I guess Siata must have used specific accessories such as wheels, door handles, steering wheels, speedometers, etc. whose brands or designs are known? Looking at your pictures that show the outside and the inside of the car, isn’t it possible to see whether these accessories are of Siata-origin or not?
- Apparently the body is made of steel, right? Were Amica’s body made of steel?
- One last -crazy- idea: why not borrow a metal detector and make sure that no pieces or clues were left on the ground after you retrieved the car? If only you could find a rusty Siata badge, it would help!