I can't be sure but I think the motors on a BP is designed be reversed with the drum switch without problems to the motor. I had a friend that used a BP to drill and tap with a non reversing tapping head for years doing 100's of holes/day with the motor connected to supplied 3 phase from power lines. I have a Cincinnati ToolMaster and have been doing the same thing that is currently connected to 240VAC single phase using a Delta wound 3HP 1140RPM (1200RPM sync speed) 3 phase motor as a converter (RPC) with a non reversing torque limiting tapping head from SPI for quite a while (over 6 years) without problems, I completed tapping 3/8-24 on 400 pieces a few months ago and the same amount has been reordered, I'm tapping them now and told in a few months they will be ordered again. However my machine motor and my friends was original as supplied my the maker and probably designed to reverse. Years ago when I had my Big shop I made a reversing switch that reversed the wiring so reverse could be done with a foot switch and tapped thousands of holes without damaging the motor. I also know where my father worked they had a few BPs tapping by reversing the spindle, he worked there for 10 years, machines were there when he got there and were still running when he left!