If you have a Lifesling aboard, you should also have the Lifesling lifting tackle to help retrieve a victim. These are either 3:1 or 5:1 blocks which attach to a halyard, or the boom to lift a victim over the lifelines, and back aboard.
You could also use the Lifesling lifting tackle in conjunction with the halyard/boom and an outboard motor lifting sling to help manage the 58lb Lehr. This should allow one person to rig the tackle, and then, easily, lift and
guide the motor to its mount.
Forgive me but, I love that I can lift my Mercury 3.3 2-stroke with one hand, because it only weighs 30lbs with a full tank of gas.