Take a photo of the tensioner, as a "test" remove all the locking pins and see if you can get it on then, I bet your struggling with pulling it tight over the locked pulleys so loose alot of slack like that when the belts sitting a tooth out. Obviously don't motor it like this! Will answer the question of if the belts long enough they do stretch with age so expect the new one to be a few mm shorter but nothing big that it wouldn't allow you to replace with a new one something's not right.
![[Image: 22f2b6b2-758b-4c1c-96fb-6fa9c6059b13_zpsf306b56b.jpg]](http://i585.photobucket.com/albums/ss299/Ha11elujaz0rs/22f2b6b2-758b-4c1c-96fb-6fa9c6059b13_zpsf306b56b.jpg)