We have had so many of the PD rocker aluminum plugs fall out, we invented a 'repair' that is just about foolproof. So, buying a replacement rocker is just about stupid when all you really need is to properly plug the galley hole.
First, there are actually 4 of the plugs; one in each end of the rocker shaft. The ones in between the two shafts can't fall out, but the thing to do is brad them into place. We hammer them home with a small, round flat punch, then with a centering punch, strike around the edges to brad the plugs into place.
The ones to the outside of the rocker shaft will blow out. Sometimes you find them; sometimes you don't. I keep several of the used camshaft cap bolts around. The 'barrel' in the center of the bolt has an unusual benefit. Although the OEM bolts are not reusable, the barrel is a press-fit to go into the galley hole of the rocker shafts. The only reason there is a plug, is to cover the hole bored in order to provide oil the rockers. Once done, there is no reason to ever go into that plugged area. Saw off the threads of the cam cap screw, hammer the barrel end into the galley hole and saw off the remainder of the screw with a hack saw. It will NEVER come out, unless you drill it out.`
So much for the rocker shaft.
I agree, in part, with Brian. If nothing else, the cylinder head and oil pan come off. Piston height, galling in cylinders, rod and main bearings needs to be checked. But the cylinder head... who knows? Maybe it's some junk from one of the Chinese purveyors of CRAP. Maybe the builder used the wrong hold down screws for the injectors. Or he didn't know how to tighten them. He sure didn't know how to install the injectors. It just might be a rebuildable head. I think I would be inclined to get a new set of my rocker bolts and 4 injector bolts. Remove all the glow plugs and make sure there is no fuel left in the cylinders. Change the oil.
Reseal the injectors and clean the burrs out of the injector bore holes. Make sure the injector hold down screw holes are not chewed up. They may need to have recoils, if buggered up. Clamp the injectors down to 78 INCH pounds... like not quite 8 ft lbs... That is tight enough to tell what compression you can get and start the car, if need be..
Horrible Freight... diesel compression tester... replace the schrader valve in the insert that is 10 x 1.0... DO NOT OVERTIGHTEN insert, as it is only brass and will strip...Charge battery to full. Disable the injector harness from the engine harness at the driver's side (round plug). Crank engine until the pressure stops rising. If all cylinders are 460psi +/- 10%, and no lower than 400psi, you got no block problem, most likely.
What you need to figure out: 1. Is the cam toast? 2. are the injectors ok? 3. is the timing belt ok? 5. Are the bearings ok? 5. Are the pistons, rods and bores ok?
In this case, I'd make sure there are no bent rods before taking giant steps like replacing the whole cylinder head. All that fuel in your oil, and worse, much of it had to go through the pistons, bearings and cylinders. There is a potential of hydrolock, bearing damage, piston damage.
We reman cylinder heads. Lots of them. As a matter of fact, we have one completed BRM cylinder head under the counter looking for a home. We also have all the parts and pieces in order to put it back together. It includes our PD cam and cylinder head modifications. So, it is not the 'wear out' cam that comes in the OEM cylinder head. If the oil was too thin, you may have damaged cam, rod or main bearings, or cylinder walls. Before you jump off into the deep end, you better make sure the engine block and body qualify for an expensive head.
Just because the injectors came out of the head doesn't mean they can't go right back in. Don't assume anything. The assumption here is that a whole bunch of parts have to be replaced. I've already staunched the bleeding with a $0 hack to fix the rocker shaft. If you strip the injector hold down holes, we repair those, too.
Good luck. You could use some.