Not mega expensive for a preamp if the last ebay sale is anything to go by ... https://www.ebay.com/itm/Harman-Kard...p2047675.l2557 I might just look out for one to play with.
I wonder how accurately RIAA is/was applied at any time.
It is impossible for anything digital to sound analogue, because it isn't analogue!
Those are the least likely to need it, if there was a stereo version. (Though as Geoff says RIAA can often be a bit variable even into the stereo era, I find DG recordings sometimes spectacularly so).
For sure I regularly find that it's not just early 50s microgroove that benefits from tweaking, stuff right into the 60s, cut and pressed on later stereo kit, can still be badly equalised. Often a recording you think is just a bad recording, flat or dull or edgy can come to life with a few subtle changes.