Cool. So far I like the CV4031. Slightly more Rp (6.8K versus 6K) and if I read the data sheet, slightly less gm. Everything else seems the same to me. Since you mentioned it, the plate dissipation is more than the 6J6 (2 x 1.6W versus 2 x 1.1W). The tubes come in nicely overdone packaging, including pin savers. I paid $12 shipped for the pair from the UK.
To me it seems like there is better bass control. And perhaps more gain, but I'd have to measure or reread your post above in light of the changes. For now, I'm resting and enjoying the amp