EDIT: I have read wrong and replied back thinking it was the previous RFT 6SN7 tubes you were still talking about....my bad haha. Btw how's the Glenn?
Are these worth the asking price?
The 12SN7 + adapter cheaper still, the same tube with a 12V heater voltage.
You can run them without the adapter and they may be fine.
I was very surprised as the 6H12C is a very rare tube, they don't turn up that often.