They are on their side, resting. Look real hard and you should find them on their side in the lifter gallery.
I had an engine that had obviously destroyed a rocker in its past, as evidenced by the dent in the valve cover. The previous owner just bought new pushrods and left the old ones down there. I wouldn't do this because the other pushrods had worn quite a bit because they were rubbing against the falling ones.
I would think you could get them out with a good flashlight and a magnet. Also check the condition of the other pushrods you might need to replace a bunch of them.
Someone else will have to reply with the fix and what to check.
•1982 GMC K2500 Cummins 4bt/NV4500/NP208