There was some tinkering going on with Rebels and early H's, some small stuff (as we've been reminded by the marketing of the new Rebellion's), but that looks like a Rebel 5.. PWK was just aiming for his usual goals with limited FR and some portability. The 3's == Shorthorns (without all the outboard filigree) and came as the first "successful" (ie not the Reb 1's) Rebels from Cabinart. The 4's came to be to have one that fit in his plane for traveling to dealers, etc, IIRC, and the 5's came later. The only real tech writing on them was in his small corner horns article in a trade pub. They're all (the Rebels) "two-humpers"....PWK said it looked like a camel-humped response. The principle was the slot to both lowpass right with the compliance which, in his way, he noted as a sort of "perverted" bass-reflex principle, but he confessed to sizing "live" during development with the mic and seeking maximum output. I broke 'em all down and analyzed the crap out of them all years ago. Not what you'd build if you're starting from scratch, but, as a sucker for old junk, I'd not have passed on that either, Congrats. I wanna say (faulty memory) he was aiming for 100Hz on-up for the 5's, but I think reality might challenge that another 15Hz. Those (5's), or some of them, rather, actually had strap handles on top and were aimed at portability for presentations. Maybe ask JRH for dating on that style of badge if none of us can nail that down.