The required belt length can vary, depending on pulley sizes.
Does the car have underdrive pulleys?
Have any of the pulleys been swapped out? For example I have a bronco ps pulley in mine.
The best solution is to measure with a piece of string, to get you close.
This has never worked on the first try for me though. I always have to go back to the parts store at least once.
use a 76 inch belt to bypass the smog pump I found the info in an official ford book. I used it on my 91 and it works fine, it's a little tight but it works.
Micro V K060775 (O'Reilys) - it's measured in millimeters and I believe it was like 2020mm or something like that, but that's the part number....right around 84 inches. You don't want it too tight and the tensioner will make up for some slack.