Hello everybody! I need advice regarding 18K4F engine.

The story began when my “mechanic” changed HD. The car run with big tappets noise and then when I put it to road the engine seized. Two camshafts stacked. When we opened the head it appeared that two camshafts welded to the HD body because lack of oil in the head. Now we removed the head in order to investigate reason. When we started to follow the oil channels and way the oils supplied to the head we noticed some strange think like a ball staked in one of the two oil holes which locates on the top of the block under the dowel. Nobody of the mechanics has seen this type of engine before but in one voice say that this ball (or something) has not to be there because it blocks main oil supply to the head of the engine. The strange thing that these engines run fine before HG was changed. Please help to identify whether this is some sort of valve or this should be removed out!
I've attached picture below.
Many Thanks in advance.

That ball is blocking the oil supply to the cam shafts. It should not be there. My guess is that it got there when the HD was off and it some how dropped in. Is it stuck tight? If it is steel try a magnet to get it out. Or you take the cam shafts off and push it out with a piece of thin rod.

Those are deep marks on the HD surface. Has it been machined to make sure it is flat?

It stacked VERY hard. We tried magnet and even compressed air to get it out. Nothing helped. Our suggestion that when the engine warmed up the hole became bigger and it failed in dipper blocking it completely when the engine cooled down. Now no idea how to remove it.

Sorry missed part. The marks are not in the head. Those are in the block. The picture shows the block side of the engine. The ball is in the block.

Do you have a Dremel tool set? You could try to grind a flat face on it then drill and tap a screw into it an pull it out.

That oil way comes up from the oil pump and is THE oil supply to the cams.