All the different advice because of all the different engines. They are not all alike nor are timing chains and tensioners all alike. Plus people have varying appetites for risk. Replacing the lower chain guides is a much bigger job than replacing just the uppers - which can be accessed by just removing the valve covers. I've heard of only one broken 119 lower guide - someone on this forum. I talked to several mechanics who have never seen a broken 119 lower. Curious if Doc has ever seen one. Problems with uppers seem to be much more common.