IF one side is dry, say 3-4 and the other is wet, 1-2, its not the oil pump. the 2 sides are fed from the same main feed from the pump. That feed splits under the cylinder and shoots up the rear studs on either side of the cam chain tunnel. The blockage usualy occurs at the orifice from the head to the cam tower. The block, usually debris froma prior overhaul, has it been worked on before you?, is forced up by oil pressure into the orifice and closes off the hole. It is possible that when the pressur relents, the plug drops back down the stud/oil passage. Waiting to be pushed back up into the hole once the pressure comes back.
Personal experience here and from many posters on the forum. This is not unique, happens a lot.
AS to your question the parts will interchange. But the later parts will have places for screws the K0 did not have. Ignore them.
