* Forecasts operating profit of Y140 bln for year to March 2020.: TOKYO (Reuters) - Toshiba Corp bowed to pressure from activist investors and said it would overhaul its board to include non-Japanese directors for the first time in 80 years, marking a dramatic shift at a cornerstone of corporate Japan. The company, in the throes of a turnaround after being roiled by a crisis stemming from the bankruptcy of its U.S. nuclear power unit, said it would hike the number of external directors on its 12-member board to 10 from seven in June.