The problem with not using the cam locks is you can't get an even tension over the length of the belt. With out using them and a dti you can't be sure that it was timed up correctly before you started on it and now it could be even further out.
I see what you're saying, but for a belt to have pulled it all a tooth out just between the banks is pretty extreme. As long as it was tight against the idler when you took it apart and it's tight against the idler when you put it back together, it's not going to be a tooth out. Once you've spun it and retensioned, it'll be accurate.
I can see the advantage of using the blocks, it removes the possibility of mistake, but the marking up method would still have worked fine in most cases and would have avoided disturbing so much of the engine....which is a bonus.
Embarrasingly for us, my friend marked the crank up on the washer behind the crank sprocket, for some reason thinking it was part of it (I trusted him, he's a damn good mechanic for Ford)...it wasn't and it moved. I didn't notice before I'd slackened off the belt....that coupled with the state of the belt that came off means I'm only 95% sure i've got it right. I wouldn't fire it up unless 100% sure....or she'd kick my ***.
If I'd been 100% sure it was perfectly at TDC when he marked it up I'd have been happy to do without the blocks. But hey, it's no biggie.
I'll happily admit, if I'd known I could rent them so easily and cheaply from up the road, I'd have got them from the beginning....but it can be reliably done without them.