Tip 0.5 (just thought of this one before posting) If you bought an MES from IBM it probably includes a free install by an IBM Engineer. Ask the people you got it from if not sure.
The cache option fits on to the adapter card in the server, not in the disk drawer / tower.
Tip 1: Label the cables before, or as, you disconnect them (they all look the same when disconnected).
You should have a memory module and a battery, it is pretty obvious where they fit, once the card is in your (ESD protected) hand.
Tip 2: If you are not familliar with ESD protection, read up on it and make sure you fully understand how to prevent it and how much it might cost you if you get it wrong.
Once installed and the server is up and running again, you will need to use the SSA service tools to enable the FWC (Fast Write Cache) for each drive you want to use it.