I guess I interpreted the question as more the nuts and bolts of the hermonies that make the "Do-wop sound"

As a matter of reality, when my do-wop group gets together and we grind out a song, we do not write the parts out, we pick a key, start vamping (in first inversion) then add lead line, bass line and stack the harmonies so they are comfortable for our inner guys. I am not a theory guy per se, but have always played and sung what sounded right. I managed to get this knowledge purely by trial and error as well as listening to the old recordings to get an idea.

It would be oversimplification to say that my formula is 100percent accurate in all do-wop music, but it will give you a running start on most oldies!