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the 3rd puts something under the side to hold it up, like a 2x4 or bricks so you can mount the bracket w/o having to keep the thing in the air. but im sure you already thought about that
but why do you need to "lift" the tub? Won't the bracket just slide under the tub and the weight of the tub hold it in place?
Lifting WITHOUT sliding is a good point. When people lift something large, like a spa, they'll tend to push into it as well. You should only need to lift it about 1/2" to slide the bracket under. I'd try a flat bar (small flat pry bar AKA wonder bar). One person should be able to step on the lat bar, lifting the spa, while another slides the bracket under.
I'm curious, if one of the small pry bars would give enough leverage? I think you want one of these: (check local tool rental shops)
At the price we paid, it better be. My wife Gina made the purchase, but it looks like a solid construction. I'll see if I can find their website.