Hi all I have been reading this thread with great interest, I have this model and made a minor changes to it I think you may want to add to your versions. Unfortunately I don't have many photos yet but it's easy to explain, it's to do with the hoist rope, currently it is operating on 2 falls (a fall = how many times the rope goes from cat head to hook block) I have increased mine to 4 falls thus reducing the strain on the hoist drum.
Please excuse the snowglobe ballast.
Another possibility for someone to try adding, the crane ability to build it's own ballast. Modern cranes load their own ballast onto what's called a castle situated on the bed of the crane once all the ballast is loaded the crane slews round and picks up the castle and ballast,watch this video to see what I mean
btw I am on the back of the trailer the ballast is being loaded onto lol