Those graphs look pretty clean, a might too clean I would say. Not that I have a 1950s RS56 laying around, but I’m going to guess it was a bit more noisy and added a bit more distortion than this plugin.
Doing some “lesser-known” brands this week. From the Boz “signature series.” David Bendeth is a pretty good signature to have, I must say. He has been making hit (and quality) recordings for about 100 years, I think. I don’t know how much input he had on this, or if they simply used his Ward-Beck Systems M462B EQ to model it.
A freebie with somewhat of a cult following. Audio damage says this has a “uniquely warm sound.” I’m not sure what’s unique about a low pass filter and loads of aliased distortion, but maybe there is something I am missing.