How long should the serpentine belt be?

Has this car had an engine swap? From the factory it has a 2.5L straight 6. The primary belt is routed the way of the first image, the red indicates the spring-loaded tensioner, you use a wrench to turn the tensioner toward the left side, then the belt goes over it and you release it, so it holds tension on the belt. Without moving the tensioner the belt will be "short" because the tensioner is in the wrong position. If the car has A/C, it will have a second belt on the front like the second image, there is a second tensioner for that belt.

https://www.2carpros.com/articles/replace-serpentine-belt