308 exhaust ansa what year?

If it fits a GTSi then its the same as a 78 up US spec car tip spacing wise, you can ask for the spacing from the center of the 2 tips to the center of the 2 tips, thats where the 77 down is wider by maybe an inch. The later injected cars had a bumper extension and a more protruding rear bumper with a different diaper so the tips might stick out further too. They made so many damn changes over the years you have to be careful.

 

I don't know if Paul is limiting his comments to just the tip spacing, but the mounting ears on that eBay ANSA will not directly fit a '78-'79 US 308 -- here's a shot of the ANSA (FE2040) that would fit your '78's stock silencer hangers:
(PS They are not always accurate, but the SPC and OM illustrations available from the Owners Site might help you identify which model/year/version a particular exhaust system would fit -- since the Seller usually doesn't have a clue )
(PPS These are non-stainless steel systems so keep that in mind price-wise.)
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I ran into a problem on my 79 where I had a 77 system on it, the outlets in the diaper were closer together so the 77 tips didnt line up with the holes and I had to MacGyver it to make it work.