Using the weight of the lintel involves either getting it up there and bringing it back down (while we raise the second upright) or else we need guy ropes capable of withstanding the 7 ton strain.

I'm concerned that such a load being taken up by the guy ropes as the levers are operated will produce enough stretch that the levers will never achieve their full pressure on the stone before they run out of movement. We need a method that can absorb the stretch in the rope first and then continue to apply movement to the stone.