Quick update - I picked up a pair of NOS Svetlana SV-2A3 (2C4C) tubes and a pair of EML mesh 2a3s.
Both will take a little bit of time to break in, but immediately fresh out of the boxes, each set sounds much better overall than the Linlai tubes that came with the amp - as to be expected.
I'll see how they develop over time!
While I'm curious about the Takatsukis, I'm not curious enough to spend the asking price on them. I have heard that their 300b tubes are sublime, but they're even more expensive (and I don't have a 300b amp haha).