Well, of course the Letterman are one of the greatest vocal groups of all-time, very MOR, very white. The Association I think would also be in that group.
Sadly, The Association tend to be rather unfairly lumped in with the MOR brigade, a result of folks only knowing The Greatest Hits collection, or the Bones Howe produced era. If only they would look beyond early '68 and check out The Association (aka Stonehenge) from 1969, Stop Your Motor from '71 or Waterbeds In Trinidad from '72.
Alternatively, just YouTube 'Pandoras Golden Heebie Jeebies'...
'nuff said...