Ok, so the original issue was convertor failed, but engine always ran hot and detonated. Pull it apart and find blown head gasket and trashed bearings. My guess of the sequence of events. Either detonation or no retorque on those head gaskets pushed the fire ring to the valley or it ran hot and crushed the head gasket and then it failed. Not that uncommon in SB mopar. Why the R block has a fifth head bolt there. I assume you are running antifreeze which is very bad for bearings. If the converter wasn’t seated would it go 500 miles? I feel the converter failed then killed the thrust bearing in addition to the antifreeze. What did the oil look like? If those are icon flat tops, The icon 20.55 cc dish piston is about 10 grams heavier than the flat top. If the crank can be turned, I would turn it, buy the appropriate bearings. Buy the dished pistons and i would have it balanced. Reuse the rods. I would clean the block to within an inch of its life using bottle brushes then do it two more times! I would run a cometic head gasket. For your target c/r it is probably overkill, but I would still do it. I measure to determine bearing clearance, that being said I still double check using plastigauge. I can slide my converter back with the trans and motor together. I spin it a bit as it slides back.
