You have my sympathy JJ I have learned by many mistakes over the last 50 years,been down your route initially,mainly because in the early day of getting my hands into engine innards hadn't the money to buy new bearings and couldn't find any engineers who could do regrinds and rebores etc so used to convice myself that the crank was ok

and shells would do.and then like you hear the dreaded death rattle again.My view now is that if an engine has developed big end or main bearing rattle,then there is a very strong chance that the shaft journals have worn oval,which will quickly knock out new shells,and need to be checked,damage like cracks and grooving is easy to see and assess,ovality needs measuring with caliper guages.And as an asside B series engines (I have mainly worked with MGBs) regularly needed a new conrod in the piston that had been knocking because the little end also got knocked oval and ripped out the new shells within 50 miles or so.So take heart many of us so called ancient experts

have been in the same situation as you,I once fitted a minor gearbox and found the thrust bearing sitting on the bench

Note must check the one I'm about to fit. GOOD LUCK