That is a lot of deflection, if it really is bending the rocker arm stud. Did you say that this was not there before? Another possibility is the the threads on the nut are jacked, the nut could be cracked. inspect or broken parts 1st bed threads in the head. If nothing is found. Clay the gap between the nut and cover, pull off and check distance. Clay again but roll the motor over a couple of times. See if the clay smears. It the nut is touching the cover try bluing the cover and bolt cover down to see the interference pattern. Blue the cover again and roll motor over and check. If you don't have bluing dye I have used permanent black marker.

i noticed that the intake rockers are not the same as the exhaust rockers.is there a reason for that?

1.7 and 1.8 ratio. one set is SS the other is chrome molly.
Just thinking here. The cover is dented at the rub point. I wonder if the stud or the lock nut are bad and the cover is holding the nut on the stud when the lobe lifts the valve. Will have to turn it over without the cover on or see if the cover moves with it on but not bolted down.

Are those pro 1 heads?

Possible the mark is from when the valve cover flexed/dented during install....and not rocker nut/stud flexing?

Yes they are Dart Pro 1's

Are you sure there isn't an issue with the rocker bosses. Those heads are notorious for that.

If memory serves me the studs had longer threads on the head side to counter that. BUT I will check for a loose stud in the boss. If it deflected that much I would think that it would have ran off the head of the valve stem.

i have used a lot of pro1 heads through the years and never had a problem with the stud bosses.if the geomitry is wrong or the valve train is unstable you can damage any brand of head.

The head has issues. It's not a myth. When you use a rocker arm the geometry is always wrong that's why there is a pattern/ sweep. What's your point? You walk on water. Have a magic wand you can wave over a valve train and it becomes perfect. Not sure what you are getting at. I on the other hand was simply trying to give the OP I different idea than what was posted by others as what to look for.