If I remember correctly, WEBN started out as a Classical/Jazz outlet that had an "underground" show on at night called "Jelly Pudding". I have no idea when WEBN went full time to the Rock format. Some other ones with longevity include:
1) KSHE - St Louis (which you mentioned)
2) WMMR - Philadelphia (late 60's and still AOR)
3) KQRS - Minneapolis/St Paul (now pretty much Classic Rock
4) KLOS - Los Angeles (1969 and now Classic Rock
5) WAAF - Boston area (they have been Rock since the late 60's or early 70's, but I think they may have gone off the rock reservation once or twice in the 70's.
6) WRIF - Detroit - Still AOR (circa 1970)
7) WDVE - Pittsburgh - primarily Classic Rock these days but they have late 60's/early 70's heritage.
8) KISS - San Antonio (Rock from 1970 -1990; flipped to Oldies in 1990, returned to Rock in 1992)
9) KISW - Seattle - Rock since 1970
10) KDKB - Phoenix - Rock since 1971
11) KBPI - Denver - Rock since the early 70's (moved from 105.9 to 106.7 in 1994)
12) WMMS - Cleveland - They started out in the late 60's, but have ventured into Top 40 and Alternative during their tenure.
dlf