You might be able to have a local welding shop fabricate H-shaped steel extension boxes that would slip over the frame rails and give you a steady point for the lift arms to engage. They don't have to be made of thick metal, probably 4MM thick steel would be plenty strong for a properly designed extender 6 inches tall or so. Let the legs of the extension extend a couple of inches over the sides of the frame rail for stability.
Jerry

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