Hold on.
Was the holding foul on Team B called? If so, then, by rule, the clock was stopped to complete that penalty. The dead-ball shoving foul occurred after the clock was stopped. That being the case, I believe the governing foul is the holding by Team B. Since Team B was behind in the score, 3-4-3 does not apply. The subsequent foul by A has no direct affect on the game clock or the play clock, since the clock was already stopped for the Team B foul. So, the clock is governed by normal rules, which means the clock starts on the Referee's signal.
Now, in the absence of the Defensive Holding foul, yes, B would get an option as to when the clock starts, due to the Team A UNR, for which the clock would have stopped.
Robert