Thanks, Roger. When it goes well, I like 12A?7- and 6S?7-based audio circuits that are flexible in that way.
As for the era of the tubes' production, though I respect anyone's decision to use modern tubes (whether for availability, cost or, as you cited, for a particular sound), I am strictly a vintage tube-o-phile. If I want more grit, I'll use a boost pedal in front of the preamp.
Also, I feel compelled to note that vintage tubes don't have to be expensive. Yes, I spent real money on some tubes. But even though I never pay dealer prices, my collection includes many rare and fine tubes. Those include some "new in box" ones; and further, a few that are so rare they "shouldn't exist" and truly are fit for a museum.
The key is knowing how to identify vintage tubes: with persistence, if 1. you know the histories and physical features, and 2. you can "see past the paint", then you can acquire some good vintage tubes at reasonable prices.
Anyway... thanks again for bringing this beautiful amplifier into the world!
