I owned, listened to and sold many of those speakers in the early 70's. The AR-KLH-Advent followed a certain lineage of Henry Kloss and the Advents easily outplayed most of the comparable box speakers in the day. The big AR3a was probably a better speaker, certainly better built, as was the KLH 5, but the Advent had a less wooly sound, at least when driven with the mediocre solid state receivers that were usually coupled with them.
AR made a 'big' speaker, called an LST, which Levinson later used in multiple sets- don't know what mods he performed on them. Those would be pretty rare, i think, and probably insanely power hungry. Most of those 'acoustic suspension' speakers were very inefficient, and were mated with solid state equipment which offered higher power and 'lower' measurable distortion.
I am not as familiar with the small Infinities of that day- their claim to fame was the multi-piece Servo-Statik, and later tower speakers with monster woofer arrays.
EV- other than horn speakers, I don't remember much in the way of bookshelf speakers in that era, except for one that was equalized, and actually sounded pretty good at the time. The name escapes me right now.
Best bet, imo, is a refreshed pair of Quad electrostats (aka- 57's) with a low powered tube amp. I switched to this kind of set up in about 1973 and never looked back. (Except recently, when I bought my first large horn set up, go figure). Good luck.
