An apparatus and a method of mounting a standard size power generating unit (30) to any one of several different sized railroad cars utilizes different sized interface blocks (28) to mate the unit to the bearing adapter blocks (14) of the cars. The axle (32) of the car includes a projection (18) extending from an end (16) thereof and the power generating unit (30) includes a frame (50) and a rotor arranged for rotation in the frame for generating the power. A drive shaft (74) is attached to the rotor and includes a follower (78) for engaging the projection (18) so that when the axle is rotated about the axis (44), the projection engages the follower and thereby rotates the rotor. The interface block (28) is disposed between the frame (50) and the bearing adapter block (14), a first surface (54) of the interface block being attached to the bearing adapter block (14) and the frame (50) being attached to a second surface (56) of the interface block opposite the first surface.