A characteristic of this movement is that the time mainspring is 3/4 inches wide, but the strike mainspring is 5/8 inches wide.
The time mainspring was stronger than necessary, 0.0177 inches thick. I replaced it with a mainspring 3/4 x 0.016 x 120 inches long, Timesavers #15959.
The original strike mainspring of 5/8 x 0.018 inches was retained in the clock.