Thank you I think you are correct. Looking online there are a bewildering number of models none of which quite look like mine ,but there is a lot of similar design featuresI think it’s an old Rotostay ,there is a grub screw in the top drum slot .Or maybe in the drum body .
.The bottom end of the torque tube joined on the alloy foil is threaded into the drum .
The slot was designed for deck sweeper genoas.