Hey, I gave them a yell ... imagine the response if we could get three people doing it, and singing a bar of Alice's Restaurant as well?
Maybe we need a "yellow sheet" copper cap mod as a sticky?
One thought (owch!) ... As mentioned, the metal container is a potential ground point for an arc. Maybe one more mod would be to spray the inside with a generous coat of PlastiDip. It's a good insulator, and if you're worried about the heat, watch this ...
(And no, I've never had a problem, but mine is strictly a backup and has maybe 50 hours on it is all ...)
Another option ... if heat is the killer, drill vent holes top and bottom. Seems to me I've seen that done ... maybe one of my better hallucinations?
As an alternative, figure out an alternate location for the can cap, and build two 5AR4's into the circuit, all whilst keeping things tidy inside the stock "dynaco" chassis. That'd even be doable in my custom chassis by adding a riser box over the single rectifier that'd be deep enough to install dual sockets ... hmmmmm ... more glow!
(I can already see a problem with me trying to drive two GZ37s with the stock iron.) ;-}