[Nigel Haslock]

If the issue is physically getting the marks to line up as you put the belt on, this might help.

This assumes that the crankshaft isn't going to move and that it is at TDC.

Wrap the belt around the crankshaft pulley.

Maintaining tension on the belt, i.e. hand tight, wrap it around the upper spocket with the upper spocket on its mark.

Keeping enough tension that it doesn't jump a tooth, bring it down to the lower sprocket.

Do a trial fit on the lower sprocket, including setting the tensioner. Count how many teeth away from the mark the sprocet is.

Remove the tensioner sprocket to free the belt, but keep tension on the belt so nothing else moves.

Move the lower sprocket the number of teeth you counted in the appropriate direction.

Ease the belt on again, set the tensioner and everything should be in the right place.