Hard to tell what the problem was. Metallury, wrong lifter pre load, wrong length of the push rod, rocker arm failure....etc.
Make sure to replace the push rod together with the rocker arm as well. Check for proper length and pre load.
Good luck

I'm gonna swap both lines of push rods...

Looks like the push rod in question was starving from insufficient oil supply. See its' dark blueish coloration beneath the tip. This possible cause would explain the tipp's abrasion.
Make sure to disassemble the rocker arm shafts and flush clean everything. The shafts can accumulate a lot of grime that can block oil flow to the rocker arms.

That sounds like a probable reason because the rocker arms on the 1:st cylinder and the valve springs were covered with a sticky mass, however i'm gonna replace as most parts as possible with new ones, mayby even the rocker shaft if it is worn out...

I have senn on pictures in this forum that the heads came in two different sizes on valves, is it anybody who had measured the different valves so I can find out wich size I got????

More pictures are on Facebook, just copy and paste my name down here and add me as a "Friend":

Tommy Myran Nyström

and explain u are from this forum an I accept it.

Check out this section. Lots of information.
viewforum.php?f=29