To the owner of the vehicle that has the spun or worn rod bearing.
Without any disrespect or prejudice towards other respondents, I believe you are being given incorrect information concerning your issue. In the event that your engine has incurred bottom end damage (a spun rod bearing is the most likely culprit) my recommendation would be to quit while you are ahead and focus on replacing this engine. The dealer's diagnosis of a spun rod bearing sounds accurate given the symptoms, and I see no evidence of wrongdoing from your head gasket mechanic, quite the contrary actually.
A head gasket can fail a number of ways, often (and as is the case with most FZJ80s) it is a case of the coolant passages becoming open to the combustion chamber. Often times this is noticeable due to white smoke emanations due to coolant being burned by the combustion process (essentially steam). However, in certain circumstances the coolant (which can now enter the combustion chamber) can leak down past the piston rings into the bottom end of the engine, diluting the engine oil. The coolant will emulsify with the oil when the engine is running and will be pumped through the oil pressure system. This is very bad as the coolant dilutes the oil and the lubrication properties go out the window. Damage to bearings can result. The reason the oil pressure drops is as the bearing or bearings wear, all the relative tolerances (space between surfaces) increases and the resistance to oil flow decreases, hence the pressure drops. The information you have been given leads me to believe that not only is a new engine required, but your technician is probably not at fault. Although I am speculating, the oil pan removal (hence oil pan gasket) was likely for inspection purposes and for cleaning out all the coolant/oil goo that was in the bottom end of the engine. It is something I quote with every head gasket job I complete when there is evidence of coolant ingress into the engine.
In addition, the technician appears adamant that it is futile to spend time and money on a dead engine. This would also be my recommendation. It is obvious that the damage is severe due to the symptoms (combination of loud noise and lack of oil pressure). Performing a post-mortem will likely only confirm the bearing damage but my not provide a clear indication of the cause of failure. Although it is not impossible to incorrectly complete a head gasket replacement and damage an engine in this manner, it is unlikely, and my opinion is that the damage was likely present prior to the head gasket replacement being performed. I am again speculating but I am guessing that the engine started behaving badly after a high speed, high load run on a highway. This is a high stress situation for an engine bottom end and any damage present would likely make itself known in such a condition.
Hope this sheds some insight into your issue. Although this constitutes an opinion that is founded on my professional training and experience as a motor vehicle technician, your mileage may vary.
