Also just finished up my drum/disc conversion on Saturday... Perhaps the rotors you have are meant for the front? The rear rotors have a larger diameter hat.
I have a couple of spare rotors kicking around here... The inside diameter of the hat on the rears is roughly 6-1/4" vs. 5-9/16" on the fronts.
From what I understand the rear hubs are the same across all cars, regardless of discs vs. drums or otherwise, so it definitely sounds like you have the wrong rotors.
