I just checked the book. The short number is the correct belt by the book. There are times you have to remove the fan, put the belts on the pully then reinstall the 4 bolts that go into the block. Some also have a second set of holes to add distance for mounting the fan higher. this could also be why they don’t fit.
Dayco makes a 54.5 and a 55.5 belt, but does not show a 55in. in the catalog. The new book has gone metric so those numbers are now 15A-1385 and 15A1410.