Thanks Coop,

But,

If the rocking produces the slack you need to install the cam sprocket, then stop to make sure the timing marks still line up.

It's possible to walk chain slack to the driver's side of the crank gear and then throw off the valve timing by "rocking" the crank too far clockwise.

If that produces enuff slack to allow install of the cam sprocket, then make sure the crank is at 0 and the cam dowel straight up and there is NO slack in the drivers side of the chain once all is fitted.