I have personally checked an engine's cam timing while assembling it,checking it as normal before the heads were on,then re checking after the 600 plus pound spring equipped heads were on and everything ready to go.The timing on this particular build with a Cloyes top of the line timing chain retarded by a solid one+ degree before even being broken in.
You can't tell me a chain won't stretch a degree or two after a few passes with a really stout set of springs working against it.
Keith