If it's rear engined, then yes it's called a Fiat 850 Sport Spider (or Convertible).
The engine capacity varied, early US versions were 817cc. There were also 843 and 903cc versions. Your's, if a '71, is probably a 903cc unit.
I'm not certain (it's been quite a while) but iirc the engine # location in on the cylinder block just above the aluminum timing chain cover, close to the generator mounting.
Hth,
AL.