Yes,
That’s tough, as one always needs to find a good cross reference which I noted earlier.
I had the same issue with 3 of my projects.
59 FC
61 FB
69 RT40 Corona
I was just very lucky that all 3 of these cars had the original spare tyres with the correct model numbers that matched the owners/service manuals. All I needed to do was take the spare tyre to a tyre shop and match up a new tyre to the old in rolling height, diameter and circumference.
If your car has the original tyres or a spare that corresponds with the manuals, you just need to do these easy checks alongside a new tyre.
If someone has done all that hard work for you, and the 195/80 R15 is a perfect match, fantastic.
Some people just like to say close enough is good enough when they advise someone else, because that’s what they may have been told third hand etc