If you plan carefully you can simply hang the chain house in the right spot from the ceiling, and place the car under it sitting on its tires. Then hoise up the engine/grbx as a unit until it clears the chassis. Once you have it clear, roll the car forward and out of the way. Now the power unit can be set on a dolly or roll away table etc and moved to the location you will work on it.
If you don't have fore-aft room in the garage then the car can be placed on those 4 caster dollies and moved sideways out of the way in the same manner.
Sometimes an overhead rail and hoist dolly takes up more vertical room than you have or is just more complicated than necessary. I have my chain hoist mounted from a steel piece of flat stock (3X16ishX1/4) hanging from a 2X12 up in the attic that crosses 8 joists on edge to spread the load. The 2X12 is braced with 6 pieces of angle iron to keep it from being pulled over on its side. The steel mounting tab is sticking down through the drywall with a nice big hole in it to hang the chain hoist from. It was a bit of work but very strong as well as not costing very much to do.