I had replaced the stock HDD on A1261 Macbook Pro 4,1 with an SSD. While this was better, I did not have enough storage. For that reason I installed a platter drive in the superdrive space and created a "Fusion Drive." Now I have 1.25 TB of storage that really screams.
It was easy, but I have experience in going in on MacBooks. The part fit exactly and required no refitting.
If you have an old MBP and want to combine better speed and more storage, give it a try.