Dog - Since your boat is an 89, I would hope it has a 25" transom. You really need a 25" shaft motor if you're gonna put it on a bracket. Don't know if it's the geometry of the bracket or the effect of the longer shaft, but when I had a 20" motor hanging on the transom, the power trim had nowhere near the effect on running angle that it does now with the bracket and longer shaft. I now use the tabs primarily for roll control and use the power trim to adjust running angle.
What size prop are you currently running and what is your max rpm/mph and min planing speed with a typical load? Any 4 blade prop will give you more stern lift than what you have now due to the extra blade, but some are made for bass boats with a lot of rake to create bow lift, which is not what you want. Look for one that's advertised for "heavy offshore boats, to help them stay on plane at lower speeds". I believe the BRP Renegade Offshore fits this description. Suggest you register on the
E-TEC Owners Forum and post your prop questions there, including type of boat, weight, intended uses, and current prop and max rpm with your typical load. It's a great website supported by a couple of really knowledgeable technicians that can give you some good advice.
I've tried the 4B Michigan Vortex (aluminum) and Apollo and a 15x15 PowerTech with the old SST blade profile. All were a big improvement over the 3B props I tried, but I like the PowerTech the best and it uses the Michigan 2-piece hub system that is more robust than that used on the Merc props. I can plane at 12-13 mph with any of these props.
FYI - here's a link to a post I made a couple years ago on the Pro's & Con's of Outboard Brackets.
Pro's & Con's of Outboard Brackets.