camrcobr

I am about to replace a leaking head gasket on my 1996 Mustang Cobra 4.6 32V engine and in reading the service manuals they say two things that seem to conflict. First they say to use a special tool to lock the cams in place before removing the heads and second it says to rotate the crankshaft counter-clockwise 90 degrees (keyway at 9 o'clock) before replacing the head on the reinstall.
The manual says this is to prevent damage....but since this is an interference engine, wouldn't this CAUSE damage?