As a straight lifting device, an A frame is easy to store and set up but is limited in its scope. Rex Chatfield had a good idea: he has set a steel tube in the ground and a solid inverted L frame with hydraulic crane jib drops into it when required. With this, one man can lift (say) a Crossley 1075 weighing a good seven hundredweight straight up by pumping at a lever. A trailer is then manoeuvred underneath and Robert is your mother's brother.
Moving across the floor horizontally - well, it depends on the surface. The little I can see of my garage/workshop floor is smooth enough, but the garden path is dreadfully uneven, so castored trolleys wouldn't work for me.
A vertical engine I would probably "walk" from corner to corner on a solid piece of plywood. You can move surprising weights that way, but be careful not to let it get away from you. A horizontal engine is more difficult, especially as they tend to be heavier than verticals. A sheet of solid ply and a crowbar will usually do it.
I have lifted half a ton before now with a crowbar and a number of decent wooden blocks, placed upon direction by a nervous Hazel - but I'll only admit to moving that sort of weight up a step etc!
In a more general way, I thoroughly recommend you to a second hand set of hydraulic sack trucks, an absolute Godsend for anyone working alone and well worth the eighty quid I paid for mine.
Regards,
Kim Siddorn