I've heard Smart Tabs work pretty well. And another forum member on here said the Bob's cav plate worked great.
With that 30 4 stroke you should be getting on plane just fine, depending on your prop. I have a Merc 25 2 stroke on my J16 that's set up very similar to yours minus the poling platform (for now ;D) and, especially if I'm by myself, I get on plane quick. I have a 10 3/8 x 13 Powertech prop.
I bought one for my Johnson 25 so I could keep water on my prop as I raised my jack plate, but after I received it I decided not to use it because it just did not fit.
I didn't like it, because it's designed for larger motors and is CUT DOWN for small motors. On some small motors it fits ok but not all .
The mounting holes would be less than 1/8" from the sides of my Johnson 25 cav plate.
I ended up making my own that I am happy with.
Then someone posted a link to this one that I like and is designed for many different motor sizes and makes.