T.J., I can help a little bit with your question, as I was the specific person who suggested that change to then-owner Interurban Radio. At the time, 940 was trying their heart out with a rap/dance music format, and while I loved hanging out with the music-loving staff in the control room @ 2222 Gravier Street, the numbers on the signal-limited AM station were just not happening. At the time, NOLA had no full-time, full-service Gospel station, and I still remember gathering up my nerve to walk into the manager's office to pitch my observation that those unbelievably-valuable WYLD call letters would be better used on a traditional urban Gospel station like the ones I grew up with in LA and MS. I also wish I had a picture of the look on my face when she said "you're right, let's change the format". A humble engineer doesn't get many chances like that in our business.
I was there in 1988-89, so your timeframe would be about right.
Also: in a funny / ironic twist I now work with one of the radio groups who are on the bleeding edge of the classic hip-hop format. "What is old is new again".