Yep - the headshell is obvious conversion, but you can also tell by the model number (_100TR). There were some RevIII heads made, but only later 2 channel versions I think (like this one, which I can't believe sold for that much; time to sell my spare Sessionman vocal, damn:
Garnet Revolution iii Vintage Tube Guitar Amp Head Serviced & Ready ) and the model name was _100D. D meaning head version of a model that was usually a combo.
Another cool score by Frenchie. And I bet he paid next to noffin for it too. Happy birthday indeed. That one at least should be easy to hide; smaller than your usual purchases.
The guitarist in one of my bands has a later 2 channel Rev III combo (2x12) and we like it a lot. He's found a new love for his Strat with it; he says it's very responsive to playing dynamics (more so than with his Tele - he never uses bridge only, which I think sounds perfect with this amp - I'm the one who found it at a local store and called him cuz it sounded so good with a random Tele they also had).
What the heck is "controlled atmosphere conditions" all about?
Anything from having HVAC (back then not so standard) - e.g. temp fluctuations could cause the springs to expand/contract so the length and therefore delay time/sound in general would not be consistant from tank to tank made at different times of year (or even day to day) - to clean room (which would be total overkill since the things aren't hermetically sealed).