Camshaft refit and timing setup

I have stripped this engine down, new cylinder head gasket and rebuilt engine. I am trying to set up the timing for the engine, but everything in manual is a little vague and confusing.
When I set all timing marks in line, the valves in number four piston will touch the piston head. There is a point in manual when it says, "to avoid accidental damage to pistons or valves, you must turn the crankshaft backwards by 60 degrees". That is the last this is mentioned, it doesn't say at any point to put it forward by the same amount, and when moved backwards by 60 degrees, it puts the timing well out. I just don't understand how, 60 degrees is a large amount to be out.
The car is a diesel 1.7 turbo.