One more, well really two more things:
1. Tungsol reissue 12AT7 are decent, almost as good as NOS Mullard and not nearly so flaky and fraught with problems.
2. Try replacing the coupling caps (C3, 4, 9 & 10) with mid grade Mundorfs. Even the standard Supreme (about at about $11 each) should provide a sonic lift. Just put 50 to 100 hours on them before judging.