Please look at this.
http://cgi.ebay.pl/ws/eBayISAPI.dll?ViewItem&item=150421973986&ssPageName=ADME:B:SS:PL:1123It is advertised and a muffler for 131 Abarth.
The tailpipe openings look ca 25mm , about half of what Abarth requires
You have to have a lot of imagination to believe this would not kill the Abarth engine, preventing it to start.
Mounting bracket would not allow to fit it under rear axle and probably make the tailpipes drag on the road making some nice (Abarth

) sparks.
Conclusion : if is says 131 Abarth on ebay : beware it maybe not quite accurate ...
Miro