Looks like back in 1997, a Technical Service Bulletin (TSB) was issued on a whole series of Ford fans, including the 94-97 Taurus/Sable, Continental, and Mark 8. It says that replacing the motor could result in "Noise/Vibration/Harshness (NVH) issues".

Seems the units are balanced at the factory, and replacing just the motor is a no-no.

HUMMER .25: No need to compensate.

1989 Dodge Raider: 3.0/5
1992 Chrysler LeBaron Convertible: 3.0/A
1994 GMC Safari: 4.3/A