Welcome back! Sounds like you've done some great research. Although I'd disagree that you need a new putter if the current one sinks putts. That one is more of a personal journey :)
You're right that blades have fundamentally not changed much, and honestly I'd doubt you'd see much difference between your Bridgestones and a modern blade, probably the best thing you'd find there would be a pretty decent shaft for you that would generally improve the experience.
Nowadays there's quite a bit higher variance in what you could consider a "cavity back" though, so if I were you I'd consider opening your horizons a bit more. Certainly there are some giga-sized loft jacked monsters out there, but outside of that you can get some traditionally lofted forged cavity back clubs that will feel and spin at least as nice as every blade you've ever played, with some of the benefits of modern perimeter weighting and forgiveness without you even noticing.
The class of clubs I'm talking about include Wilson Staff CBs, Mizunos JPX921/JPX923 line, Taylormade P7CBs, Cobra CBs, maybe even the Titleist T100, etc
i think you'd be doing yourself a massive disservice completely writing off modern players irons like that before you even hit them.