Mark the belt with white or silver permanent pen. Release the auto tensioner and remove the belt. Set the timing marks up where they are supposed to be, and put the belt back on with a new tensioner. The whole point of the timing marks is so you can remove the belt and put new ones on without having to worry about where everything used to be. As long as they all line up you are fine. Make sure the lines you made on the belt line up perfectly with the correct marks on each of the pulleys and gears, etc.

Once you get it together again, see if you can rotate the assembly.

That is the best you can do without removing the head for now. Sorry.