I also put a 3TB WD Red WD30EFRX into a refurbished 2 TB Time Capsule and it was hours of tedious work. Cutting the rubber bumpers to fit took a couple tries, and somehow the alignment shifted during all this so that the top metal plate took considerable force to line up, and the ports are still a little more recessed than they should be.

My reason for doing this was to move the disk from my old TC (the previous generation), but in retrospect I wish I had just bought a 3 TB Time Capsule and copied the files over. Not recommended.