WNCI became a Top 40 in 1970, give or take a year. That's the same time (or about the same time) they switched from mono to stereo and took on the moniker Stereo 98, with a logo that incorporated the Peace Dove. They were not a tight-listed station back then. To the contrary, they had an even longer and broader list than then-kingpin WCOL-AM, whose list was laready considered long by early 70's standards. Instead of a Top 40 (plus some "hitbounds") like COL, NCI had the "Hot Half Hundred"of 50 songs, plus a lot of extras. Their evenings were devoted to "progressive rock" album cuts, via "E. Karl's Incredible Progressive Rock Circus".
In mid-1975, under the direction of consultant Bartell Media, NCI did a major flip-flop to a super-tight list. That's when Michael O'Malley came in for mornings, and Steve Edwards (who has been the voice of Jeg's "forever") came in for afternoons. They also cut the spotload. This new approach quickly wiped COL-AM off the map, a number of years before the big AM Top 40's in other markets had to concede the format to FM.
I think Terry Tyler (formerly of NCI) joined a year or two later. He was good. As for John L, I always get confused here...I know there was a John L on the '70-'75 NCI, and maybe even later, but I'm not sure whether it's the same John Lane who was later on 'TVN.
Back with an edit: O'Malley may have actually started a little before the 1975 tightening at NCI. Before O'Malley it was Charlie Pickard, whose voice should be very familiar because of the huge number of TV and radio voiceovers he's done in the past 30 years. If you don't know the name, listen to some samples on the link below and you'll probably recognize the voice. His laid-back style was very characteristic of NCI's pre-1975 "progressive" approach to Top 40.
http://hearvoices.com/charlie-pickard.html