I've never seen a sbc pump "loose prime" if it had been primed correctly. To put the rear main bearing in they would have had to drop the oil pump. Had they not disturbed it too much it probably still would have had oil in it. But I've been known to pull the cover off and pack the gears with petroleum jelly as to make sure it's got something in there. Reinstalling the pump they could have broken the plastic sleeve on the end of the oil pump driveshaft which could cause issues.
Ideally after doing a bearing job I would have pre-lubed the system by running a drill on the oil pump to make sure the pump built pressure. Obviously they did not do that here. Had they done that they would have found the lack of pressure without turning the engine over and having to do the bearing job a second time.
Why the bearings were wiped out after 135k miles is a good question though. If it was a bearing clearance issue I would think the pressure would have gotten less over time and not all at once. So why would it drop all of the sudden? Oil pump failure? Pump driveshaft failure? Leaked oil out? But it stands to reason once the pressure went away that's when the bearings got scored up. So did they go after the symptom of no oil pressure and fixed the bearings but not find the cause? Probably. With the bearings in the first time and not fixing the cause they fired it up and no oil pressure still. At that point they had to backtrack to find why it had no pressure. It's my best guess at what might have happened.
Bearings wiping out is a factor of loss of lubrication or too tight or loose setup. The engine mounts would not cause this issue at all.
Ideally after doing a bearing job I would have pre-lubed the system by running a drill on the oil pump to make sure the pump built pressure. Obviously they did not do that here. Had they done that they would have found the lack of pressure without turning the engine over and having to do the bearing job a second time.
Why the bearings were wiped out after 135k miles is a good question though. If it was a bearing clearance issue I would think the pressure would have gotten less over time and not all at once. So why would it drop all of the sudden? Oil pump failure? Pump driveshaft failure? Leaked oil out? But it stands to reason once the pressure went away that's when the bearings got scored up. So did they go after the symptom of no oil pressure and fixed the bearings but not find the cause? Probably. With the bearings in the first time and not fixing the cause they fired it up and no oil pressure still. At that point they had to backtrack to find why it had no pressure. It's my best guess at what might have happened.
Bearings wiping out is a factor of loss of lubrication or too tight or loose setup. The engine mounts would not cause this issue at all.

coming from this guy again .