Install used engine - done 6hrs of your life.

remove head and/or oil pan - 8/12 hrs of your life. and the possibility of it grenading afterwards. not to mention all the fricken gaskets and new bolts.

yes, the head and rocker bolts must be replaced as they are torque to yield crap.

And if it helps any the oil pan is a PITA to remove with the engina in the car.