[Brian in Tucson]

I had mine up that high when I swapped my engine. Y'all are right, it is fairly unstable. I used stacked 2x8 slabs as insurance to catch it when it came off the jackstands Mine moved laterally. Several times, scared the heck out of me.

The other thing is that when the engine/trans is lowered to the furniture dolly, I reinforced mine with 3/4 inch plywood, it's very important to keep the assembly strapped to the dolly. Ratcheting motorcycle straps work really well for this.

There are two of the bolts that hold the trans to the rear of the engine on top. I used one of these to drop the engine with my cherry picker. You need something on the front of the engine, too, I used a loop of webbing around the power steering pump pulley and then hooked onto it with a second lift chain.