Turning the crank pulley 1/2 a tooth anticlockwise from the TDC position before threading up over the non-adjustable idler to cams 4 and 3 is the key. Otherwise, you will almost always be a tooth out on this run, IME.
Crank back to TDC and check there's no slack in this run then round the eccentric idler, cams 2 and 1 and onto the sprung tensioner.
Set the eccentric idler to remove any slack in the run between the 2 banks then put the correct tension on the tensioner, remove locking kit and turn it over 2 turns and re-check timing and tension, adjusting the eccentric if cams 1 and 2 are out. Repeat as required.
If you've got marks on the belt it's easy to see if you've dropped a tooth between any of the pullies while threading the belt. Without the markings you need to be extra careful that the belt runs are tight.
It also helps if the locking kit fits well. Some have a little slop in the cam pulley locks which doesn't help matters. Don't attempt it without a locking kit.
The procedure in the Haynes manual has never made any sense to me. It makes me wonder if they actually did the job or just looked at the pictures and wrote what they thought the procedure would be, so disregard this and follow the DVD.

Kevin