The cats were considered Throw Away engines as they can not be overhauled in place.
The block does not have removable liners , so must be removed to bore the cast cylinders over sized.
The big labor is R&R the entire engine , not the work required to rebuild it.
Look up Jasper and see if they still have rebuilt 3208 , at least you will get a ball park on the rebuild cost.
The R&R cost will depend on how well the boat was designed.