Most GO-Fast boats are going to have either Bravo Ones or Bravo XR's.
The XR's are supposedly a little tougher than the Bravo 1's but the guys on here still manage to break anything Mercury throws at them.
All Bravo Variants will not have transmissions inside the boat, they will be in the drive itself.
Bravo III's are dual props, but you rarely see them on Go-Fast boats - they are usually on cruisers.
Alpha's are weaker drives that you will usually see behind Small Blocks.
TRS are tougher older drives that Mercury no longer makes. They have tranmissions inside the boat that attach to the back of the engine.
Drive Showers are nothing more than a little mechanism that shoots water up and drops it on top of the drive - they help cool the transmission that is in the top of Bravo and Alpha drives.