Rebuilder did not completely remove the cosmoline from new bearings, resulting in high initial friction and heat? Rebuilder used old surplus bearings that had surface corrosion? Dirty/plugged journal feed to this bearing at overhaul? Failed to apply overhaul (thick) lubricate to this bearing at overhaul? Installed a 0.003" over bearing in a standard journal? Moisture and acid damage will generally be prevalent throughout, very noticeable in valve covers as rust and green slime....your block looks clean, free of moisture and acid. Good luck!