Okay so - I think I've arrived at a solution. The (previously hull mounted) blocks that I thought were Harken were 40mm Ronstan units that definitely do not ratchet. I'm planning on moving the 57mm ratchamatics to the hull position and I've ordered a pair of 57mm carbo ratchamatics for the beam. This combination should make it much easier to sheet the spinnaker. I will report back on how well this works.