I've been grappling with this question too. This may well be my only engine rebuild, so I didn't want to buy a bunch of expensive stuff for single use. My current plan, untested as yet, is shown below (I was literally just planning this tonight). I strengthened a standard (maybe slightly small) pallet across both ends and through the middle, and added some strong casters (the same ones that I used on my now dismantled chassis stand) to make a dolly. I'll prop the dolly up on jackstands right up under the engine on the stand. This is too high for my floor jack, but starting with the jack on an i-beam, I should be able to lower it in just a couple stops to the floor. Then under the car it goes.
I believe I could do this myself, but will have 2 or 3 people at hand when the time comes to help stabilize the dolly on the jack.
I'll probably be doing this beginning of next week, and can let you know how it goes.
Mike