The concrete blocks can be made safer also, by a piece of plywood on top and bottom. It will serve to cushion the block and prevent fracturing from point - pressure.

Better yet, if you have some of those 2X4s left over, make a solid lift block by nailing them in perpendicular layers.

Speaking of the 2X4s, your body dolly looks pretty stout, but might benefit from some cross bracing.

Good start on the project.