J/30 Class Association Forums J/30 Forum The Boat, Sails and Equipment Main Halyard Sheaves

I need to replace the Main Halyard Sheaves. Does anyone know where I might find drawings or dimensions for them? I have a crew memeber who is machinist that is going to make them out of Stainless Steel with Ball Bearings pressed in. Would like to only have to go up the mast one time to remove old and replace new.
Capt Bob