I am contemplating swapping back and forth 2 engines in my 67 911 to accommodate an electronic fuel injection experiment. The swap problem you ask about rang my bell. My idea follows
Suppose you built a wood 2x4 dolly with 4 wheels to hold the engine and/or transmission high enough to allow lowering the car onto the dolly with the engine installed so that the wheels are off the ground. Then remove the bolts holding the engine -transmission to the car. Then jack/lift the car off the engine, roll the engine/transmission away from the car.
I have built a wood 2x4 rolling engine running stand which holds my test engine. I'm not ready yet for the swap but will have to address the one-man swap technique soon.
What do you think?