I dunno if you need spacers.
Just look at the offset value stamped on each wheel... it's the number after the letters ET.
The bigger the offset number the more "in" the wheel arch the wheel would be, so ET40 would be 5mm further into the wheel arch (which reduces the track) than an ET35 wheel.
So.. if your Cinq wheels are ET35 and the Abarth wheels are ET38 say, then you would need 3mm spacers to restore the original track.
On the other hand.. 3mm is not even noticeable in real life, so you could also leave it without spacers, as long as the wheel doesn't foul the calipers etc (unlikely but possible).
Anything more than 5mm difference in ET, then use spacers.
Ralf S.