Anode current 450-630 mA is insanity! I did notice the spec sheet says "Working position: upright" whereas the amp designers have positioned it horizontally. I've never been a fan of output tubes mounted this way, I can see that cooking one side of the tube and killing it stone dead very quickly and I wouldn't care to be around one when the tube starts arcing and shorting.
Most valves are fine with horizontal mounting.
Usually the datasheet specifies an orientation for horizontal mounting so that the part of the anode that gets hot is at either side of the valve (rather than top an bottom).
Regardless, I consider a horizontally mounted valves in a well ventilated box, a la Bluesbreaker, to be better for thermal management than valves mounted upside down, as in Fender combos.
