Chris
I am quite sure that the car is a Racing Volumetrico.
First because what Simon says. Genuine Abarths have AR in the chassisnumber.
Second because you talk about a serie from 100 pieces. That is the story published a few times in several magazines about the 131Volumetrico( actually about the Supermirafiori but they also show the Racing). Read my story here in the history part to know more about these interesting cars.
The car is, if what I tell here, is correct indeed special and in my opinion NOT a good base for another reproduction
.
A genuine Racing Volumetrico wears on the typeplate AK V1 and has enginenumber 232R10.
Simon: Racing Volumetrico is AK V1, Supermira Volumetrico A2V2
The Volumetrico range was only for a short while on offer on the italian market. If my info is correct 1 car was exported new to France and it didn't survive.
Please show us pictures
Albert