I have been a varsity HS R for about 20 years now. Our crew's U works D3 U, as well. He's as good as they come.
We always agree on the starting point and stopping point of a penalty enforcement (we're going from the 23 to the 38) before we split to do our thing. Sometimes he talks, sometimes I do. We both know what we're doing pretty well, but there can't be enough checks as we go along -- and it takes an extra 5 seconds at most. Then while I'm reporting the foul, he signals the yardage (1, 2, or 3 fingers) to the wing and has one wing holding the enforcement spot and the other going to the succeeding spot. The B, unless he's doing something else, is recording the foul -- he normally gets what he needs through the radios.
Now, if it's a false start or the like, it's prelim-ed to me, I signal from where I am standing, and the U spots it and we're ready for play. All single flag fouls are prelim-ed and numbers communicated over the radios.
If there's anything I've learned the hard way is that you can't communicate too much. I'm sure he would have the yardage right without our step of agreeing between the two of us, but it works well for us.