We have P&W 901A's on our 747-400's.
The elec generators are driven by the N1 (load) gearbox. There are no Constant Speed Drives on this type, so N1 is kept close to 100% (8000rpm). N2 varies, depending on loads. The starter and accessory geabox is on the N2. The accessory gearbox drives the oil and fuel pumps.
Rgds.
NSEU