If the lifters are mushroomed, pulling them up thru the lifter bores will gouge and scar the lifter bores. If it can be determined that the camshaft has worn a lobe or two off,which it is appearing that is the case, the engine will need to be completely disassembled anyway. You might be able to insert an inspection mirror into the fuel pump hole(remove fuel pump), and see(with flashlight) if you can see the lobes at the front of the cam, or at least closest to the pump hole. If camshaft damage is evident, then with the engine upside down on a stand, the lifters can be pushed down far enough to remove the camshaft, and then knocked back into the bores from the top side, eliminating the possible damage to the bores. As an extra step, you could cut the oil filter open and see if there are excess amounts of trash in it, revealing evidence of parts failure. Good luck....
