Got caught by this once. Started with some bare heads and labored all the way to the point of installing the opening rockers - and could not do it! Why won’t they fit? I calmly asked myself. Someone thought the opening rockers needed that little notch to be installed. So they cast one in, but put both on the same side, instead of where the rockers actually went - on opposite sides. But it really didn’t seem to matter till i had installed one of the several Pantah race cams - with bigger lobes and higher lift. Correction needed. Break out the Dremel tool. And even then you must grind out the groove much more than the interior recess. The head is a 1982 casting; Ducati noticed and corrected the problem later. Also, you can see where the triangular slicers at the top have been ground off; leave those on while you fight installing the closer spring and see what it gets you. MikeV

Well that's an easy one to solve if you follow the parts book. Rocker arm 0660.92.170 is for the early heads and 0660.92.173 for the later heads that have the cast in hump. Yes if putting the later beefier rockers in the earlier heads you gotta do some grinding.
-Cranky-

Yep. That is what it was Cranky. And shortened even more so they could be moved over, using the clip, instead of removed in order to adjust the shims. The original cast-in recess is, still, odd. MikeV