@roxy54: Are you thinking of the FMI (Fulton Musical Industries) Model J loudspeaker? It was comprised of three separate boxes: on the bottom a transmisionline-loaded woofer enclosure, in the middle a small sealed enclosure with an 8" woofer and dome tweeter (marketed separately as the Model 80), and on top an RTR ESL tweeter array (6 ESL tweeters per side iirc)---the same tweeter Dave Wilson used in his original WAMM loudspeaker. I bought a pair of the Model J in 1974, when it was priced at $1200/pr. JGH loved it, putting the Model J at the top of his recommended component list.
Before ESS introduced the Heil AMT loudspeaker, their flagship model was the TranStatic I, which was also a three way: a KEF B139 woofer in a transmissionline enclosure, a KEF B110 5" cone midrange, and three of the RTR ESL tweeters mentioned above. It retailed in the early-70’s for $599/each, and was competition for the Infinity Servo-Static I. I have a pair sitting in my spare room.