That looks like a newer Dominator bowl to me.  If that is in fact a Dominator bowl, you are stoked!  You will need to pull the droop to grease the bowl bushings (or to see if it is water lubed), please post a picture of the outlet vanes of the pump bowl, it might already be done up nice.  It would be worth it for you to pull the bowl to see what impeller you have and just do an overall inspection of the pump while the engine is out.

Yes, that Place Diverter & Controls droop is intended to work with a bolt-on ride plate.

http://www.placediverter.com/proddetail.php?prod=place_diverter_droop_snoot

The bolt-on ride plate will not give you the same performance or tunability as a shoe/ride plate.  Be advised that in order to install a shoe and ride plate, you will need to pull & reset your intake.  Not a small task just before the season starts in a new (to you) boat.  Being that you already have trim plates installed, I am not sure how much a real ride plate will help you, but the tenability of a shoe will definitely benefit you.

My suggestion, get it wet and see what it does.  A different engine with different horsepower will affect how the boat handles.  If you have an opportunity to dyno your engine, use the uncorrected (observed) horsepower to help select an impeller cut.

Cheers,

Joe