I think most of you guys are guilty of a serious case of overcomplicating, assuming that the OP's machinery moving exploits are at most an occasional thing. He's got the simplest solution implied in his post. Lift the machine off the pallet with the chain fall, which I will assume is at a fixed location. Set the machine on the ground. Now use the engine hoist to spot the machine in its final location. Yes, it's two steps not one, but NO modifications or re-engineering of machines is needed, and NO unsafe or questionable practices are needed. To move a dozen or so machines, I doubt the extra steps will add one hour to tne entire project time, whereas rejiggering the hoist will consume several times that.
Johnson bars are great and have their place, but I can't quite see how it will help if you have a machine set well within the perimieter of the pallet. Also, the OP mentions top heavy. Johnson bars tip things, and that could be unpleasant if the machine is tipped the wrong way.
In one instance I had a machine on a pallet and I wanted to leave it on the pallet for a while. The pallet was too big, and the machine didn't occupy the entire area. I was able to take a Sawzall to the pallet and give it a haircut until the size suited my needs. Basically, I cut it down from a three-stringer pallet to a two-stringer pallet. OP, you may be able to chop up some pallets, too, to allow clearance for your hoist.
I have several heavy machines that see only occasional use, and require quite a bit of acreage when in use. I store these machines on the sidelines, on pieces of 4x4's, until they are needed, then I use the pallet jack to move them around, and spot them on more 4 x 4's while in use (not top heavy). I suppose if I were more organized, I would tie the 4x4's to the machines with lag screws, so I don't have to repositon them every time, but this works and it's simple.
Pallet jacks are a cure for world hunger. For fifty bucks you can easily and safely move two and a half tons. Everybody should have at least one!
Steve
btw, re: shop cranes with legs that splay: I have two of these, a two ton and a three ton, both Rugers, and I seriously doubt that the legs on the three ton will splay wide enough to clear a standard 42" pallet. I'm certain the two ton won't.