The engine is a big lump with all the ancilliaries. The heavier duty the crane, the easier it is. Getting the motor coupled back onto the gearbox and the splines lined up can be very fiddly. I tried on my own at first with no success, and needed another 2 pairs of hands to get the engine fully back onto the gearbox, with me beneath the vehicle, and a couple of mates up top............and an engine leveller helps on the crane.
With the jib extended out, they tend to bounce a bit. You dont want any trapped fingers when you are trying to push it home. I used quite an old Clarke 1tonne crane, but it was quite heavy duty, where as some of the newer ones are a bit flimsy...........get the most robust one you can, and a decent jack under the gearbox helps to level things up.