The aluminum is probably indeed a spacer and was mounted directly to the waterpump.
What you will see with a fan clutch is that the clutch has a shaft that goes through the center hole of the fan. The fan attaches to the clutch and is flush mounted to the rear of the clutch. The clutch then mounts to the waterpump with 4 relatively short bolts.
At the end of the day, it will look like this. 4 bolts to secure fan to back side of clutch and 4 bolt that go through the 4 holes in the mounting base of the clutch and into the waterpump nose.
