This looks like a Pflueger Sea King 2188 Surf Casting Reel. This is what they usually look like...
The part that has been added on is either a two speed conversion, effectively giving the reel a high and low gear - high for reeling in fast and low for fighting fish OR it increases the gear ratio of the reel allowing it to retrieve more line per turn of the handle. If it is a two speed device there will be some mechanism on it to "shift" gears. Being that this reel was designed for surf fishing - long distance casting - both conversions would be useful during the time this reel was made. I do not believe this is a Pfluger partbut an aftermarket add-on. I have been collecting and repairing reels for over 20 years and have seen similar "add-on" devices like this, but not this particular one.
