I can't offer a yes or no opinion, but I will offer some food for thought. ..... First, if you want to see how the boat sits at rest with the heavier engine, have a 150 pound person go as far to the back of the boat as they safely can. If they can sit on top of the engine cover, that's how your boat will sit. .... As far as the engine pod (that canoe shaped piece with the transom on the back) you'll need a trained and experienced person to look at it. When I decided to repower my old 24' two log pontoon boat with a much heavier engine, I realized the original engine pod was inadequate for three reasons. First, it was old and had already had fatigue cracks rewelded. Second, the transom was made of wood and did not appear sturdy enough to handle the twisting torque the engine produces when under power. And third, the cross beams supporting the engine pod did not appear strong enough to support either the weight of the engine or the torque. So I shopped around and found a used engine pod that was much sturdier. I added some aluminum angle crossmembers to support it better and it worked out well. But that engine pod was a little heavier that the original so the rear of the boat sat even lower in the water at rest. .... My bottom line is that it is possible to put a much heavier 90 on your boat, but you may be much happier with a 4-cycle 60 as ahicks suggested.
