They're visually very different, of course, but alledgedly the lead channels are only a few resistors here and there and a few wires moved around apart. Mesa was just going for what's apparently a VERY different tone, lol. And this is a guy who builds amps as a hobby- he seems to know what he's talking about.
Don't get me wrong, barring the Road King i tried out I have yet to meet a rectifier I wasn't underwhelmed with. But the circuitry isn't far off, from the sound of it- I could just do without most of the changes they've made (Rectifiers don't really sound that great without the gain well over half up, and by that point it's far too saturated for any dynamics to be left in your signal, imo)
-D