Sounds like you have a high flotation style bracket which simply means it is larger and displaces more water when your not on plane. Once you're on plane though, the bracket is out of the water and doing nothing to help you, and this is when the extra weight KILLS your performance. Think of it like a see saw, fat kid on one side skinny kid on the other. What happens? The fat kid will go down and the skinny kid goes sky high. Same thing with a boat. The stern is heavy and goes down, while your bow goes for the sky which results in you having to use alot of negative engine trim and trim tabs to keep it down to get on plane and go level which results in excess drag and a LOSS in performance. Unless your bracket is built into the hull and made structural into the hull to extend the whole boat hull, then the bracket will only amplify the see saw effect of a heavy engine hanging on the stern.
When the V-20 was designed, the biggest outbaords weighed in around 400 pounds or less as all you had was a 200HP flywheel rated outboard back then. And the 235 OMC became the XP(175HP) in 86 when OMC went to propshaft ratings across the board. The 235HP GULPED fuel like no tommorrow, weighed in around 375-385 pounds, and made decent power(around 235 at the flywheel), but it pales in comparison power and weight wise to even an 86 225HP OMC. And like mentioned before, 4 strokes normally have the weight rating on them as just the engine without oils, propeller, and some engine manufacturers were even stripping the alternators off when stating there weights to make them sound lighter. A good example was the first large VERADOS that came out. I believe MERCURY said they weighed in at 580 pounds, but actually weighed in at close to 700 when rigged on a boat. That is about what 2 of the 235's weigh.
If you want a new engine I would limit it to a 175 SUZUKI(the 140 is a better option as it is a bit lighter), the 150 HONDA, or the 150 YAMAHA. As for 2 strokes, I would consider a 175 ETEC(the 200 small block is a good choice, but it is more of a performance oriented engine), or a 150 OPTIMAX(there is a 175 2.5L, but it is a PRO XS performance built engine).