PeterT
I performed the musical Forever Plaid, which has extremely complex harmonies( actually a bit more lush then the original arrangements) and have since written 2 shows which were basically reviews of 50s 60s do-wop.

I think it is pretty obvious that there is a lead line, then a bass part that has pretty big interval jumps sometimes a showy bass part is a nice effect. The main thing that seperates Do-wop from barbershop harmony is tha fact that generally speaking, Do-wop chords are 1st inversion for the tonic chord, while Barbershop normally follows a 2nd inversion tonic. this creates the three chord progression (in do-wop) Key of C: tonic chord EGC   4chord FAC back to tonic EGC   Dominant BDG or BDG BDFG (7th) mess with this harmony arrangement on a piano to hear the voicings and you will see that it follows the sound that the Do-wops had mist likely by accident by the way.
Once you learn to sing this, you can nearly always get the arrangement vocally in a big hurry. It just starts to make sense.

The other Chord progression that is used a lot is the Tonic, Harmonic minor Subdominant or 4 chord, followed by the Dominant seventh. Use similar voicing for inner harmonies, let the bass voice walk down, C, A, F, G (kinda like the heart and soul left hand) PM me if you would like some atrrangements and I will be glad to share what I have. I am writing another review for next May which will use this very basic arrangement for lots and lots of songs. jimmyt