Just do it. Given the old belt was intact and everything was lined up before you loosened the tensioner, if you have NOT rotated the crankshaft or cam pulleys after you removed the belt all you have to do is pull them back to the marks, clip them, line up the marks on the crank and pull the pin on the tensioner. The relationship between cams and crank will be maintained and you'll be good to go. This horse has been flogged a few times (sorry!) but bottom line is the engine is happy whether you line it up per Isuzu's instructions or per Bart's intructions.

It would still be prudent, however, to do as the manual says and rotate the engine by hand a couple revolutions to make sure there's no interference before you put the spark plugs back in and fire it up. Better safe than sorry!