How they did it is one thing but getting it on the air on two different frequencies is epic.
There are commercially available
general coverage SSB tranceivers for much less money than in years past. They are generally QRP but that's not a big hindrance if you have the $$$ for some amplification (which also is pretty cheap, especially if you are handy at building kits).
Then there is plenty of info on general-coverage modifications for some of the more popular ham rigs. One that comes to mind is the Yeasu FT-817 (and maybe the FT-818?); remove a few co-located SMD resistors and you are in business, if I recall correctly.
So the frequency agility doesn't knock my socks off. Some of the "regulars" on 43 meters (e.g., WDOG and Thunder Chicken Radio) have been known to show up on 31 meters (or so) occasionally.
Had "Art Bell" been on two frequencies
simultaneously, that would have been more impressive to me.
