Yes, the format of WBBM-FM was "adult contemporary" for most of the 70's. The station did not flip from Progressive Rock to Top 40. They were "Soft Rock 96" during the mid and late 70's, similar to today's WLIT or WCFS. I remember on a TV commercial for WBBM-FM there was a transistor radio with a plastic mold of '96' (or was it the shape of the call letters?) that was given away to listeners. That would be a very interesting collectible to own.
I did not listen to the station much, but I remember that Greg Brown was there (prior to working at WMET when the the station was Top 40), and Tony Phillips was on 6-10 at night. I remember Mitch Michaels was at WBBM-FM briefly before the flip to Top 40.
I don't much about Steve King before he worked at WLS. At WLS, I think his show started at 10 PM, after John Landecker. After Steve King left WLS, he did mornings in the same building at Disco-DAI.
WMET was never "adult rock". The station was Top 40 as WDHF and later WMET during most of the 70's. They flipped to AOR (album oriented rock) around 1978-1979. The album rock lasted until the mid 80's when they flipped to "adult contemporary" for a short time keeping the same call letters. They flipped again to a "oldies/classic hits" hybrid as WRXR, which also did not last long.
I remember when WMET was album rock, the PD that came after Bob Coburn decided to use the phrase "Chicago's Classic Rock" which was not true because the station played about 50% newer/current music. When Doubleday owned WMET around 1985 some genius-consultant from another market decided to mix-in CHR with the AOR. The would bounce from Flashdance to Led Zeppelin to Lionel Richie! WDAI and WLUP also had flings mixing in CHR cuts when they were supposed to be AOR.