If you expect that much flooding, I'd be more concerned how to avoid or minimize that in the first place!

Nevertheless, a frame of pressure treated wood anchored into the floor with concrete screws and a 1/2" min. ply wood base is the safest arrangement. Then anchor the washer into the base in case it decides to take a walk.

Forget blocks. Reminds me of all those geniuses crushed under their vehicles because they wanted to save the $20 for jack stands.

Be sure your receptacles or breakers are GFI protected!

And don't do your laundry in your hip waders.

Elevating a top-loader could make it hard to reach down to the bottom of the tub, especially for a short person. I'm not convinced it's necessary. Are there any water-sensitive components near the bottom of the cabinet?

I was thinking of elevating my dryer only, with a pallet.