If you’re still looking for information I’d suggest pull the drivers, photo the part numbers usually noted on the rear of the driver and submit to Madisound. They also carry a reasonable selection of accessories and electronics that might work for you.
I too have a pair of Kienker Neel floor standing speakers, "kni-40"-see attached pdf. I acquired my pair in 1985 from Cedric Neel. I had the bass driver surrounds replaced 10-15 years ago after the original surround started, de-laminating from the poly cone. Relatively inexpensive and easy fix. Any reputable speaker re-builder should be able to source replacement surrounds.
Both Fred Kienker(electronics) and Cedric Neel(box designer) are/were brother's-in-law to me. They teamed up to design/manufactured a line of flat response, transmission lines in the classic sense at Cedric's place in Fayetteville, Arkansas in the early ‘80s.
Cedric grew up in Hope, Arkansas and was an acquaintance of Paul Klipsh and Bob Morse. Cedric passed away a few years ago in Tulsa OK. He did recalled the 8” bass drivers being Gefco and the tweeters were Vifa, at least in my case. Fred is still around but has had no association with the business since it was dissolved in the early ‘90s.
As a side note Cedric Neel's living room housed two Klipshorn and four Heresy ( in quadrophonic arrangement-I can’t recall the preamp stage) driven by mono Crown(valve) amps and reel to reel at the source. He really enjoyed sharing his musical experiences with whoever was interested.