In my opinion, although B3 can legally step OOB following a made basket, once he sets a screen it seems to me like he is not in a position to set a legal screen. Similar to a defensive player trying to take a charge with a foot OOB (and yes I understand the difference that B3 can legally step OOB). I would interpret the play (if B gains a definite advantage or someone goes to the floor) that B3 cannot set a legal screen with a foot OOB.
If anyone here can discredit my interpretation I will be willing to hear it. It is a very interesting scenario I have not thought of before. It would reallly help to see it (from the stands at a camp and be able to listen to the evaluator's thoughts

)