Last time I ordered them they were only supplying the shorter ones and now supply an aluminum shim to install between the cover and the cam if you have their tall ones. This removes there liability of claiming it was their fault
The middle screw is for the Ducati tool that threads in and locks the cams in place for cam timing adjustment. There is a slot in the cam that the tool fits into. You would loosen the three screws on the cam pulley wheels, then lock the cams in place with the motor at TDC horizontal cylinder, then lock the cams with the tool. Next re-tighten the 3 pulley screws. Finally remove the tool and Done. Luckily the NCR covers you want use a pointed head set screw that will work the same as the Ducati tool when simply screwed in. PLEASE do not forget to back the screws out flush with the covers when done or you will do some damage if you try to start it like that. Make sure and use some thread sealer on the NCR set screw to avoid oil weeping.
Also when you change the belts you will find that the Vertical intake cam will
move when you take off the belt. Ca Cycle works makes this tool if you remove
the center screw and screw this in it will lock the cam in place.