Thanks for posting those pictures, that has clarified things quite a bit. Item 4 is called "Shaft Collar" (part number GT628) and is a simple spacer of the correct width to place the bevel gear in correct mesh with the mating gear sector on the cross shaft. It is held in place by a grub screw, Item 5. You can either buy one from Greenfield, or make one from a piece of bar or heavy-wall tube. You could obtain a price for a steering wheel from Greenfield as well, though you can probably obtain something suitable second-hand.
