I know at least for other types of roots blowers, 6-71 through 12-71, used on dragsters, that the gear drive in the blower uses 75w90 or similar final drive type gear oil. This is because of the high pressure addatives that the gears need.
Since the blowers on our cars are based off these old roots type blowers I am going to assume that they will also use the thicker oil. You might be able to use amsoil 75w90 synthetic gear oil or something similar but I think I would just stick to the GM, Eaton, Magnuesson oil.
1989 LE Bonne 122,000 miles
Custom Open Element filter system, Strut Tower Brace from 2nd gen bonne
Light Up Pontiac symbol in grill, 16 wheels from newer Bonne/G, performance tires, performance ignition system, Upgraded brakes.