Section 8.2 and 8.3 cover this as penalties by b on a touchdown are always enforced on the ensuing kickoff but since there is no kickoff they will be enforced on the try
This is logical because we don't even know yet if there will be an overtime or not....
If b comitts a foul on the try those penalties can carry over because they are enforced from the succeeding spot.
a) They aren't
always enforced on the ensuing kickoff, as there is the option to enforce on the try
b) The scenario takes place during overtime, not the down in which time expires for the fourth quarter, so yes there will be overtime because we're in it already
However, I believe that article is incorrect in its interpretation. A foul by B on a touchdown scoring play can be assessed on the try or subsequent kickoff, and since there is no kickoff the only option is the try. On page 88 of the rule book there is an interpretation, 3.1.1.A, with an USC foul after a touchdown but before the try. The only enforcement option in this scenario is on the succeeding spot -- the try. A foul by B during a successful try or field goal can be enforced at the succeeding spot as well, the first play of the next series.
Finally, NFHS has a suggested procedure for resolving tied games, but it is not required to be followed. State associations are free to "accept it as written, amended, or rejected, in whole or part", so your local overtime procedures may vary and allow the penalty to be bridged as described in the article.