Shaft extension or mounting bracket or what?

[dh2009]

Hello, this is my first time owning a boat. I have a 1980 Mercury 90Hp outboard mounted to a 1979 Monark McFast 150. The boat and transom are pretty solid. The motor has a 25" shaft, but I'm told the motor is still too short. I need have it 3-5 inches lower. I saw online where I can get a shaft extension kit, and I saw a site that sell mounting brackets. I have attached a picture of a mounting bracket they are selling (on the green/white boat). Which is better to use? Are there other means of having the motor lower in the water that may be cheaper? Thanks! (The blue boat with the motor is the boat I am still working on)