Heavy Duty Starter Motor as fitted to 4.6 Litre engines.
Will also fit
Range Rover 3.5,3.9 & 4.2
Land Rover Discovery 3.5,3.9
Range Rover 4.0 and 4.6
These units have the starter solenoid mounted to the side so may not be suitaqble for MGB V8 for example. However since these units are smaller than the OE Sd1 fit there may be sufficient space.
A measurement from the side of the engine block starter mounting to the outside edge of the starter solenoid = 1.75 inches.