Calcs are good.
For V8, 28.7 mA x 425.5V = 12.2 Watts Anode dissipation in a tube which has a data book rating of 12 Watts anode dissipation.
So it is a bit hot but not that unusual.
The culprit here is the B+ voltage which is 25V above the "typical" 400V
I would be inclined to back the idle current off - ideally both tubes (if perfectly balanced) should have around 20mA with a B+ of 425V
You could leave the bias a bit hot but back of the bias pot to get say 24 mA in V8 (the hottest tube) which is about 5.4 volts where you currently see 6.5V.
Of course I 'm a bit obsessive and have a heap of 6V6 so I would be looking for a better balanced pair of 6V6 first but that is in "nitpicking" territory.