Bayern, who travel to Israel to play Maccabi Haifa on Tuesday, notched a second successive victory after coming from behind at Dortmund's Westfalen Stadion.
Bayern now face Maccabi Haifa in the Champions League on Wednesday with their qualification hopes hanging by a thread and van Gaal under more pressure.
Grant brings with him a wealth of experience having successfully managed both Maccabi Tel Aviv and Maccabi Haifa in his homeland, while also coaching the Israel national side.
Sir Irvine was vice-president of the Sheffield Jewish Congregation and Centre, life president of Sheffield Jewish Representative Council, and a former national vice-chairman of the Maccabi sports and youth organisation.
Following a successful first spell with Maccabi Tel Aviv from 1991 to 1995, Grant engineered a return to the club in 1996 after forging a friendship with the new owner.
Henshall starred for Swindon in the famous Milk Cup youth tournament in Northern Ireland this summer, where a hat-trick against Maccabi Tel Aviv helped earn him the most valuable player award in the junior section.